GB2131628A

GB2131628A - Magnetically tuned resonant circuit

Info

Publication number: GB2131628A
Application number: GB08330702A
Authority: GB
Inventors: Ronald E Blight; Ernst F R A Schloemann
Original assignee: Raytheon Co
Current assignee: Raytheon Co
Priority date: 1982-12-03
Filing date: 1983-11-17
Publication date: 1984-06-20
Also published as: GB2131628B; US4543543A; FR2537345A1; FR2537345B1; GB8330702D0

Description

1

SPECIFICATION

Magnetically tuned resonant circuit This invention relates generally to radio frequency 70 circuits and more particularly to tunable radio fre quency resonant circuits.

As is known in the art, tunable radio frequency resonant circuits such as tunable radio frequency filters are often used in radio frequency receivers to 75 selectively transfer certain radio frequency (r.f.) sig nalstherethrough. In particular, bandpassfilters having a narrowfrequency passbandwhich may be tuned over a wide range of radio frequencies are often employed in r.f. receivers. Previously, such r.f. filters 80 were provided by using an approach such as voltage tuned back biased diodes. Such an approach was inadequatefor many receiver applications, for many reasons, but particularly as a result of its high insertion loss characteristic. A second approach, used 85 in the prior artto overcome this insertion loss probl em, is the use of magnetically tuned resonant circuits comprised of bodies of ferrimagnetic mate rials which, in the presence of a magneticfield, provides a resonantfrequency circuit. A sphere of 90 yttrium iron garnet (YIG) is often employed as the ferrimagnetic body. In prior art so-called Y1G filters, for example, generallytwo coupling loops, one coupling loop disposed about an X axis and one coupling loop disposed about a Y axis are provided with a Y1G 95 sphere disposed within both loops. Generally, each coupling loop is a conductorshaped as a semicircle with each conductor loop being disposed around a different portion of the Y1G sphere. Thiswire looptype Y1G filter solved many of the problems associated with 100 the prior art insertion loss characteristics of the voltage tuned back biased diodes. The principle of operation when using Y1G as a resonant material is that in the presence of a suitably applied DC or steady magnetic field intensity HDc, a single crystal body of such material responds to an input r.f. signal, if the input signal has a frequency component substantially equal to the resonant frequency coo of the sphere. The resonantfrequency (wo) of such a Y1G sphere in a uniform resonance mode, is given as to. V HDC, 110 where co, isthe centerband resonant radian frequency inthe uniform resonance mode, V is a quantity which is a function of the material, and is generally referred to asthe "gyromagnetic ratio", and HDC is the magnitude of the applied DC magneticfield. An r.f. signal fed to an input one of the aforementioned coupling loops, herethe X axis loop is coupled through theYIG body, to the output one of the coupling loops, herethe Y axis loop, if thefrequency of such input r.f. signal equalsthe resonantfrequency of 120 the Y1G circuit given by co, = y HDC. In operation in the uniform resonance mode,the external magneticfield HDC is applied in a direction along a Z axis aligning the spins of the electrons in the Y1G sphere along the Z axis, and the input microwave frequency signal is fed to the input loop disposed aboutthe X axis. In the presence of the external magneticfield, the resonant frequency energyfed to the input X axis loop is absorbed bythe spins of the electrons in theYIG material making the electrons precess at the resonant 130 GB 2 131 628 A 1 frequency w. aboutthe Zaxis. In responseto such precession, an RF magnetic moment is produced aboutthe Y axisthereof, which induces a current in the Y axis coupling loop as described in an article entitled - Magnetically Tunable Microwave Filters Using Single Crystal Yttrium Iron Garnet Resonators- by Philip S. Carter, Transactions on MicrowaveTheory and Techniques, Volume 9, May 1961, pp 252-260.

It has also been found thatthe resonant frequency of the above-described uniform resonance mode is a function of temperature for most orientations of the Y1G sphere with respectto the external magnetic field HDc. However, along selected well-known orientations of the crystal log raphic structure of the sphere relative to the DC magneticfield, it is also well- known thatthe resonant frequency is substantially invariant with temperature variations. Generally, in the prior art, an initially orientated Y1G sphere is disposed between the coupling loops and, in the presence of such loops, an iterative process is used where the resonant frequency of thefilter is measured with the filter operating over the temperature range, and the sphere'sfinal orientation is established when thevariation in resonantfrequency is a minimum overthe temperature range. This multi-step process is a time consuming process sincetwo alignment steps are required. It isthus a goal of Y1G filter design to provide a Y1G filter coupling structures having a controlled spatial relation to each other, and easy accessto disposed therein a Y1G sphere having a properfinal orientation to minimize temperature variations in the resonant frequency of the output signal overthe operating range of temperatures.

Further, an additional problem with the prior artY[G fitter structure isthatthe r.f. magneticfield in the vicinity of the Y1G sphere is generally not uniform. Becausethe r.f. magnetic field through the Y1G sphere is notuniform even ifthedc magneticfield HDCiS uniform,the electrons intheYIG spherewill not oscillate in phasewith each other,andthe resulting phase differences encourage, in additiontothe desired uniform resonance mode, undesirable higher order resonant modes of operation often referred to as 11 magnetostatic resonance modes" to occur. It is generally th ought that these magnetostatic resonance modes resuitfrom nonuniform motion of the magnetization within the ferrimagnetic sample and resulting dipole interaction between the magnetic moments, dueto the nonuniform distribution of thefield throughoutthe Y1G sphere. The strength of the magnetostatic resonance modes is dependent upon the shape of the resonant body, the distribution through the resonant body of the d.c. magneticfield, and the distribution of the r.f. magnetiefield through the resonant body. Coupling in such modes permits the transfer of spurious energy signals which are outside the desired narrow passband of the resonant circuit. In general, the resonant frequency of the magnetostatic resonant modes differs from that of the uniform mode by an amountwhich is proportional to the saturation magnetization M. of the material comprising the sphere resonator, here the Y1G sphere. Thus, the resonant frequency for all modes (the uniform mode as well as nonuniform modes) is given by w. = V (Hr)c + C4nM.), where 4nM. is the saturation 2 GB 2 131628 A 2 magnetization and jr.stantthat is differentfor different modes, and equals zeroforthe uniform mode.

In the prijorart, magnetostatic resonance is often surpressed in Y1G filters, forexample, bythe use of a dual stage filterwith a first Y1G sphere being a pure Y1G crystal and a second Y1G sphere being a doped Y1G crystal. Gallium doping of a Y1G crystal is often usedto changethevalue of the saturaflon magnefiza- tion, and thusto changethe nonuniform resonant frequencyof the doped Y1G spherewhile in the presence of the same d.c. magneticfield HDc as the pure Y1G sphere. The dual-stage filter is carefully designed such that each one of theYIG spheres will suppress the unwanted spurious energy produced by the other one of the Y1G spheres. Further, certain applications where -steep skiW'(i.e. sharp cutoff frequency characteristics) filter response is required, additional stages are often used to provide the desired response. If, in orderto surpress spurious energy a doped Y1G crystal is used, the insertion loss ofthe filter is increased since doping of a Y1G crystal, in general, provides a relatively lossy resonator in comparison to a pureY]G crystal. Further, where a single stage filter has a resonance characteristic which is adequate to providethe desired--- steepskiW'filter characteristics, the use of a single stage filter is generally inadequate to surpress spurious energy transfer and thus a dual stage filter as described above is often employed. This is a costly approach in terms of increased circuit complexity and increased insertion loss and thus not a very desirable solution.

An additional problem in the art isthe effectthat a conductive surface, such as the coupling loops or an r.f. conductive housing ofthe filter, has on the resonance frequency of the Y1G sphere. When a Y1G sphere is located proximate to such a conductive surface, as in most prior art structures, there is a change in the resonantfrequency of the MG sphere.

This change occurs because the proximity ofthe conductive surface to the Y1G sphere distorts the r.f. magneficfield associated with the precessing spins of the electrons, and causethe magneticfield atthe surface ofthe conductive surfaceto be in a direction parallel to theconductime surface. Normally, if thefield were not distorted,the r.f. magneticfield in such cases would have components which are perpendicular and parallel to the conductive surface. This distortion of the r.L magneticfield is caused bythe high conductim- ity of the conductivity ofthe conductive surface and results in a shift in the resonantfrequency. While at a selected temperature this -frequency shifC'can be compensated by changing the strength of the d.c. magneticfield HM this -frequency shift" is also temperature dependent making the compensation thereof more difficult over an extended temperature range. An additional problem occurs when, in responseto the varying distorted r.f. magneticfield, a voltage is induced in the conductive surface and, in responsethereto, eddy currents are produced. Since the conductive surface is not a perfect conductor, it has some dissipative characteristics and the eddy currents induced therein will dissipate power, resulting in the so-called---eddycurrent line broadening" effect. This so-called---eddycurrent line broadening- effect results in power dissipation, thereby increasing the insertion loss of the resonant circuit. In the prior art, eddy current line broadening is z duced by placing the Y1G sphere furtherfrom the conductive surface, since the power dissipated in the conductive surface has previously been found to vary as lld 4 where d is the distance between the conductive surface and the center of the Y1G sphere. However, this solution generally results in reduced coupling efficiencyand consequently unsatisfactoryfilter performance.

In accordance with the present invention, a magnetically tuned resonant circuit includes a pair of spaced coupling circuitsfor coupling energyfed to an input one of such coupling circuitsto an output one-of such coupling circuits through a resonant body disposed therebetween. Each coupling circuit includes a pair of spaced conductors. With such an arrangement, when r.f. energy isfedto an input one of such coupling circuits, the r.f. magnetic field component of such r.f.

energy has a substantially uniform spatial distribution throughoutthe region wherein the resonant body is disposed, and, as a result of such a uniform distribufion, the excitation of nonuniform modes of resonance generally associated with prior art structures is reduced, thereby reducing the coupling of spurious energythrough the resonant circuit In accordance with an additional aspect ofthe present invention, a magnetically tuned resonant circuit includes a pair of microstrip transmission lines.

Each microstrip transmission line has a strip conductor and a ground plane conductor separated by a dielectric. The ground plane conductor of each transmission line section has a selected portion thereof removed to expose a portion ofthe underlying dielectric. The ground plane conductors ofthe microstrip transmission lines are joined together along a common plane with the strip conductors of the pairof microstrip transmission linesbeing disposedon opposite sides of the common plane. The exposed portion of the substrate through each ground plane conductor surface providesa commonvoid between such combined ground plane conductors. An aperture is provided through the dielectric of both transmission line sections, such aperture being aligned with the common void. A resonant body is disposed in the aperture such thatthe strip conductor is disposed adjaceritthe resonant body. With such an arrangement, the so-called -frequency shiff'effect, which results when a resonant body is positioned adjacent a conductive surface is substantially eliminated, since here the r.f. magneticfield associated with the spins of electrons in the resonant body is generated substanfially parallel to the ground plane conductorthereby reducing the distortion of the r.f. magneticf#eld associated with the ground plane conductor. Further, the voids provided in the ground plane are preferably sufficiently large to reduce induced eddy currents thus reducing the so-called---eddycurrent line brozidening" effeetwhich generally increases insertion loss atthe resonantfrequency. This reduction of the "eddy current line broadening- effect is accomplished without significantly changing the coupling efficiency of the resonant circuit.

In accordance with an additional aspect of the present invention, a magneticallytuned resonant 3 GB 2 131 628 A 3 circuit includes a pairof spaced coupling circuitswith a resonant body disposed between such coupling circuits for coupling resonant frequency energy be tween such coupling circuitsthrough the resonant body. Each coupling circuitincludes a plurality of 70 spaced conductors arranged to provide a selected spatial distribution of the r.f. magneticfield compo nent of such resonant frequency energyfed to such coupling circuits. With such an arrangement, the spatial distribution of the r.f. magneticfield may be 75 selected to provide, incombination with spatial characteristics of the resonant body, reduced coupling to nonuniform resonance modes and hence reduced coupling of spurious energy concomitanttherewith.

In accordance with an additional aspect of the 80 present invention, a magnetically tuned resonant circuit includes a pair of microstrip transmission lines, each having a strip conductor and a dielectric, and each sharing a common ground plane conductor.

Each strip conductor has a bifurcated portion, and 85 such bifurcated portion of one of the pairof strip conductors is orthogonally aligned with the bifurcated portion with the otherone of the strip conductors. An aperture is provided through the substrate portions of such transmission lines in the region of such bifur- 90 cated portions, and a resonant body is disposed therein, between such bifurcated portions. With such an arrangement, the bifurcated portions of the pair of strip conductors enable selective shaping (orspatial distribution) of the r.f. magneticfield in the vicinity of 95 the resonant body to reduce transmission of spurious signals through the magnetically tuned resonant circuit. Further, such a structure allowsfor easy access forthe disposition therein of a resonant body with the final, desired, predetermined crystallographic orienta- 100 tion relative to a cl.c. magneticfield to enable the structure to produce an output signal having a resonant frequency substantially invariant with temperature variations over an operating range of temperatures.

The foregoing features of the invention, as well as the invention itself, maybe more fully understood from the following detailed description read together with the accompanying drawings, in which:

FIG. 1 is an exploded isometric view of a magnetical- 110 lytuned resonant circuit; FIG. 2 is an isometric view of the magnetically tuned resonant circuit shown in FIG. 1; FIG. 3 is a cross-sectional view of FIG. 2 taken along lines3-3; FIG. 4isa diagrammatical view depicting unwanted coupling of magnetic flux lines between input and output tra nsm issio n lines of the magneticallytuned resonant circuit of FIG. 1; FIGS. 5-7 are isometricviews of alternate embodiments of the invention with parts common to FIGS. 1-3 shown in phantom; FIG. 8 is an isometricview of the magneticallytuned resonantcircuit of FIG. 2 disposed in a housing; FIG. 9 is an exploded isometricview of a four channel dual-stage filter; FIG. 10 is an isometricviewof the magnetically tuned resonant circuitshown in FIG. 9; FIG. 11 is an exploded isometrieview of a magneti- callytuned resonant circuit having coupling circuits for selectively shaping an r.f. magneticfield in the region adjacent a resonant body; FIG. 12 is an isometric view of the magnetically tuned resonant circuit shown in FIG. 11; FIG. 13 is a cross-sectional view of FIG. 12 taken along lines 13-13 wherein the circuit is disposed between a magnetic pole piece and flux return yoke; FIG. 14 is a cliagrammatical view of FIG. 13 graphically showing the relationship of the r.f. magne tic fields and the resonant body;

FIG. 15 is a block diagram of a typical system application for a magnetically tuned resonant body, such asthat shown in FIG. 3 or FIG. 13; FIG. 16 is a diagrammatical view of a surface of the magneticallytuned resonant circuit, as shown in FIG.

13, detailing certain geometric relationships which are useful in understanding certain features of the inven tion; FIGS. 17-17A are a series of graphs useful in understanding certain features of the invention; FIG. 18 is an exploded isometric view of a dual-stage magneticallytuned resonantcircuit having coupling circuits for selectively shaping the r.f. magneticfield in the region adjacent a resonant body; FIG. 19 is an isometric view of the dual-stage magnetically tuned resonant circuit shown in FIG. 18; FIG. 20 is a cross-sectional viewof FIG. 19taken along lines 20-20 wherein the circuit is disposed between a magnetic pole piece and a f lux return yoke; FIG. 21 is a plan view of the single stage magnetical lytuned resonanteircuit disposed in a housing; FIG. 22 is an exploded isometricview of a magneti callytuned resonant circuit having a pulse field coil;

FIG. 23 is an isometric view of the magnetically tuned resonant circuit having a pulse field coil shown in FIG. 22; FIG. 23A is a cross-sectional view along line 23A-23A of FIG. 23 of a portion of the magnetically tuned resonant circuit; FIG. 24 is a cross-sectional view of FIG. 23 taken along lines 24-24wherein the circuit is disposed between a magnetic pole piece and a flux return yoke; FIG. 25 is a diagrammatic view of FIG. 24 graphically showing the relationship of the r.f. magneticfield, the

D.C. magnetiefields andthe resonant body;

FIG. 26 is a block diagram of a typical application for a magneticallytuned resonant circuit having a pulse field coil, such as that shown in FIG. 23;

FIG. 27 is an exploded isometricview of a dual-stage magnetically tuned resonant circuit having a pulse field coil in accordance with the invention; FIG. 28 is an isometric view of the dual-stage magnetically tuned resonant circuit as shown in FIG. 27; 120 FIG. 29 is a cross-sectional view of FIG. 28taken along lines 29-29 wherein the circuit is disposed between a magnetic pole piece and a flux return yoke; FIG. 30 is a plan view of the magneticallytuned resonant circuit shown in FIG. 23 disposed in a housing; FIGS. 31-33 are a series of plan views of alternate configurations of pulsefield current paths provided in accordancewith the invention;

FIG. 34 is an exploded isometricview of an alternate embodiment of a mag netical ly tuned resonant circuit 4 having a pulsefield coil;

FIG. 35 is an isometricview of the embodiment shown in FIG. 34; FIG. 36 is a cross-sectional view of FIG. 35 taken along lines 36-36 wherein the circuit is disposed between the 70 magnetic pole piece and flux return yoke; FIG. 37 is an exploded plan viewof a coil used in the alternate embodiment of the invention shown in FIG.

35; FIG. 38 is a schematic diagram of a drive circuit used 75 to produce a pulse of current to drive the pulse field coil;

FIG. 39 is a graphic depicting typical timing relationship used in a typical application of the invention such asthe system shown in FIG. 26; FIG. 40 is an exploded isometricview of an alternate embodiment of a dualstage magnetically tuned resonant circuitwith a pulsed field coil;

FIG. 41 is an isometric viewof the embodiment shown in FIG. 40; FIG. 42 is a cross-sectional view of FIG. 41 taken along lines 42-42; FIG. 43 is an isometricview of an apparatusfor orientating Y1G spheres; FIG. 44 is a plan view of a platform portion of the apparatus shown in FIG. 43; and FIG. 45 is a cross-sectional view taken along lines 45-45 of the platform shown in FIG. 44.

Referring nowto FIGS. 1-3, a dual-stage magnetical- lytuned resonant circuit 9 here a bandpass filter fabricated in accordance with teachings of the present invention is shown.

Referring firstto FIG. 1, the magnetically tuned resonantcircuit 9 in the presence of a magneticfield

HDC generated disposing the circuit between a magne- 100 tic pole piece 60a (FIG. 3) and flux return yoke 60b (FIG.

3) is shown to include an inputloutput coplanar waveguide (CPW) transmission line section 30 having input CPWtransmission line 33a and output CPW transmission line 30b formed on a common substrate 105 32, and an interstage CPWtransmission line section 10 having an interstage ^transmission line 18 formed on a substrate 2. Input transmission line 33a couples resonant energyto output transmission line 33b through a pair of spheres 26a, 26b comprised of a 110 ferrimagnetic material and the interstage transmis sion line 18, in a mannerto be described. The interstage coplanarwaveguide (CPW) transmission line section 10 includes the dielectric substrate 12 and a ground plane conductor 14formed on one surface 115 thereof. The ground plane conductor 14 is plated out to the periphery of the dielectric 12 to provide continuity between the ground plane 14 and a housing such as shown in FIGS. 3 and 8. Selected portions of the ground plane conductor 14 are removed to expose 120 underlying portions of the substrate 12 and thus provide a pair of elongated, parallel slots 15,1Win such ground plane 14 using conventional photolithog raphic masking and etching techniques. Such slots 15, Whave a width w, and a length 1. The slots 15,15'are 125 separated by an unetched portion of the ground plane conductor 14, here an elongated strip conductor portion 16 having a width W. The strip conductor portion 16 is here formed integ rally with the ground plane conductor 14to provide short circuits at each 130 GB 2 131628 A 4 terminal portion 17,17'of the elongated strip conductor region 16.

Terminations of the strip conductew portion 16 to the ground plane 14 are provided here in orderto generate a current maximum so as to maximize the magneticfield component of electromagnetic energy propogating along such CPWtransmission line section 10 in a mannerto be described hereinafter. Suffice itto say here, however, that the width wof each slot 15,1Win the ground plane conductor 14,thethickness h and dielectric constant of the substrate 12 andthe width w'of the strip conductor portion 16 are chosen to provide the CPWtransmission line 10 with a predetermined characteristic impedance Z, as is well-known in the art.

The magnetically tuned resonant circuit 9 is shown to further include a dielectric spacer 20, here a dielectric substrate 22, having a thickness substantially equal to the thickness of the aforementioned substrate 12 and having a pair of apertures 24a, 24b provided through a portion of the substrate 22. The pair of ferrimagnetic spheres 26a, 26b are predisposed in such apertures 24a, 24b. The first ferrimagnetic sphere26a is chosen to be comprised of a pure single crystal of yttrium iron garnet (YIG), andthe second sphere 26b is chosen to be comprised of a doped single crystal of yttrium iron garnet. The second Y1G sphere 26b is here suitably doped with a dopantsuch as gallium, in orderto changethe saturation magne- tization of such sphere in orderto suppress unwanted spurious energywhich may be coupled through such magnetically tuned resonant circuit 9, as is known in theart.

The mag netical ly tuned resonant circuit 9 is shown to also include an inputloutput (110) CPWtransmission line section 30. 110 transmission line section 30 is shown to include a ground plane conductor 34 formed on a first surface of a dielectric substrate 32. Thus, substrates 12,22 and 32 provide a composite dielectric support structure. The ground plane conductor34 is plated outto the periphery of the dielectric substrate 32 to provide continuity between the ground plane 34, the ground plane 14 and the housing 70 (FIGS. 3,8). Thus, a composite ground plane conductor 52 is provided as shown in FIG. 3. Selective portions of the ground plane conductor34 are removed to expose underlying portions of the substrate 32, providing elongated parallel slots 35a, 35a'and 35b, 35Win such ground plane conductor 14, each one of such slots 35a, 35a', 35b, 35Where having a width W. In a similar manner as described above, here pairs of such slots 35a, 3Wand 35b'35b'provide one of a pair of elongated strip conductor portions 36a, 36bformed from unetched portions of the ground plane conductor 34 disposed between slots 35a, 35a', 35b, 35W. Each one of such strip conductors has a f irst end 37a, 37b, here terminated at the edge portion of the substrate for external connection, and a second end 3M, 37b'terminated in said g round plane conductor 34. In a similar manner as previously described, the ends 3M, 37Wof each one of such strip conductors 36a, 36b isterminated with the ground plane 34to provide at such ends 3M, 37Wa short circuit in order to maximize current at such ends 3M, 37Wand hence to maximize at such ends 3M, 37b'the magnetiefield

GB 2 131 628 A 5 component of such electromagnetic energy propagat ing between such strip conductors 36a, 36b and ground plane conductor34 in orderto strongly couple the magnetic field component of such energy in a mannerto be described. As also previously described, the width W of each slot35a, 35a', 35b, 35b'in the ground plane conductor34, the thickness and dielec tric constant of the substrate 32, and thewidth Wof each strip conductor portion 36a, 36b are chosen to provide each one of the pair of CM transmission lines 75 33a, 33b with a predetermined characteristic impe dance Z., as is well-known in the art.

As shown in FIGS. 2,3, the interstage CM transmis sion line 10 is joined with the dielectric substrate 22 having the Y1G spheres 26a, 26b mounted therein such 80 as with a suitable low loss epoxy, and the inputloutput transmission line section 30. Each of such substrates 12,22 and 32 are arranged such that each Y1G sphere 26a, 26b disposed within such corresponding aperture 24a, 24b is coaxially aligned, and disposed adjacent 85 the terminations 3M, M'of strip conductor portions 36a, 36b in the ground plane 34 of inputtransmission line 33a and output tranmission line 36a, 36b, and with theterminations 17,17'of the strip conductor portions 16 of interstage CPWtransmission line section 10. The 90 substrates 12,22 and 32 arefurther arranged such that strip conductor portion 36a of input transmission line 33a is orthogonally aligned with strip conductor portion 16 of interstage transmission line section 10, and strip conductor portion 36b of outputtransmis- 95 sion line 33b is likewise orthogonaNy aligned with the strip conductor 16 of interstage transmission line 10.

Further, the apertures 24a, 24b provided in interstage substrate 22 are aligned with the region wherein the aforementioned strip conductors orthogonally cross 100 each other. As previously described, Y1G spheres 26a, 26b are disposed in the apertures 24a, 24b priorto assembly of the substrates 12, 22,32 into the mag netical ly tuned resonant circuit 9. Preferably, such Y1G spheres 26a, 26b are orientated to provide a 105 predetermined relationship between a selected crys tallog raphic direction of such Y1G spheres 26a, 26b and the external magneticfield HDC, in orderto reduce variations in a radian resonant frequency (co,,) of such spheres 26a, 26b, in the presence of such magnetic 110 field HDC, with variations in external temperature. Any method to provide an orientated Y1G sphere 26a. 26b may be used. A preferred procedure is described hereinafter in conjunction with FIG.43to FIG. 45.

Coupling of a selected portion of a radio frequency signal fed stripconductor portion 36a of input transmission line 33a to strip conductor portion 36b of outputtransmission line 33b will now be described. As shown in FIG. 3, the external dc magnetic field H+c12 is generated by disposing the magneticallytuned resonant circuit 9 between a magnetic pole piece 60a, connected to a magneticflux return yoke 60 (a portion shown) with such field HDc being applied normal to the surface of the ground plane conductors 14,34 of the magnetically tuned resonant circuit 9. Radio frequency energy in the presence of the dc magnetic field HDC is fed to here input CPWtransmission line 33a, via a connector72a (FIG. 8). As previously described, a short circuit is provided atthe opposite end of strip conductor 36a by integrally forming or terminating such strip conductor 36a with the ground plane conductor 34. A short circuit is provided in such region in order to strongly couple the magnetic field component of the radio frequency energy fed to the input transmission line section through the Y1G sphere 26a and to the interstage transmission line section 10. In the absence of a Y1G sphere disposed in aperture 24a, 24b, input radio frequency energy fed to strip conductor 36a is not coupled to the interstage transmission line 10 since the input transmission line 36a and the interstage transmission line 16 are orthogonally oriented with respectto each other. With the Y1G sphere disposed in aperture 24a, a portion of the energy fed on the strip conductor36a is absorbed bythe Y1G sphere 26a. The radian frequency 0), (hereinafter frequency) of this absorbed energy is given as o),, = y HDCwhere y is a quantity referred to as, ---thegyromagnetic ratio- and is defined as the ratio of angular momentum and magnetic moment of a spinning electron in a crystal of a ferrimagnetic material in the presence of an applied dc magnetic field, and HDC is the magnitude of the applied dc magneticfield, as previously described. Nonresonant frequency energywhich is not absorbed by the Y1G sphere 26a is reflected backwards towardsthe input source. Energy transfer between the inputtransmission line section 33a and the Y1G sphere 26a is thus possible when the frequency coi of the input radio frequency signal fed thereto is equal to the natural resonant frequency w. of the Y1G sphere as defined by the equation coi = co,. When this resonant condition is satisfied (coi = co.), the magneticfield component H, of input energyfed to the input transmission line 33a having a frequency nearthe resonant frequency co. is coupled to the spins of the electrons in the Y1G sphere 26a by making the electrons precess abouttheir-Z axis. Precession of the electrons about their-Z-axis produces, in response thereto, a radiofrequency magnetic moment about their Y axis, enabling coupling of radio frequency energy to interstagetransmission line section 10 along strip conductor 16which is disposed along the Y axis. Provided at afirstend 17 of strip conductor portion 16 is a second shortcircuit again usedto strongly couple the magneticfield componentof the radio frequency energy coupled throughtheYIG sphere 26a, as previously described. There is also sometransferof energy having a frequencywhich deviatesfrom o),,the resonant frequency. The strength of coupling of such energy and hencethe bandwidth of the coupling thereof is determined bythe proximity of thefrequencyof such energytothe resonant frequency. Radiofrequency energy coupled to strip conductor 16 of interstage transmission line section 10 propagates between the strip conductor portion 16 and the ground plane 14to the region of strip conductor portion 16 where there is a second short and wherethe second Y1G sphere 26b is disposed in the aperture 24b provided in the substrate 22. As previously described, a short circuit is provided atthe end 17'of strip conductor 16 to strongly couple the magnetiefield component of the radio frequency energyfed thereto. In a similar manner, as previously described, substantially all the energyfed along strip conductor 16 is transferred to the spins of the electrons in the second Y1G sphere 26b 6 and, in a similar manner, as previously described, such energy is then coupled to strip conductor 36b of output tra nsmissio n line section 33b.

As is well-known in the art, the resonant frequency of the Y1G sphere in the presence of a dc magnetic field 70

HDC is a strong function of variations in temperature for most orientations of the Y1G sphere crystallog raphic structure as previously described. However, along selected well-known orientations of Y1G sphere's crystallographic structure with respectto the magneticfield HDC, such resonant frequency is sub stantially invariant with temperature variations over a wide operating range of temperature. Thus, the Y1G spheres are here orientated along one of such preferred crystal lographic orientations, priorto dis posing them in such apertures 24a, 24b. Since the above-described coupling structures are planar struc turesfabricated using photolithographic techniques, theY1G sphere may be orientated priorto insertion in the filter. Thus, such Y1G spheres may be orientated in relatively large numbers to facilitate Y1G filterfabrica tion unlike prior art structures where, dueto the Referring nowto FIG. 6, an alternate embodiment of uncertainties of the spatial arrangement of the loop a magnetically tuned resonant circuit 9" is shown to type coupling circuit, such pre-orientation of a Y1G include a pair of dielectric spacers 20a', 20b'used to sphere was generally not possible. 90 hold in place the Y1G spheres 26a, 26b. Here such Referring nowto FIGS. 5,6 and 7, alternate spacer 20a', 20b'are joined to interstage section 10 embodiments of the magnetically tuned resonant and inputtoutput section 30to provide a slot41 for circuitg are shown. As shown in FIG. 5, an alternate slidably disposing therein a conductor stub 42 for embodiment 9'includes an inputloutput transmission increasing isolation between Y1G spheres 24a and line section 30'joined with the interstage section 10 95 24b. Further, here each dielectric support hasformed (FIG. 1) shown in phantom and dielectricYIG spacer 20 therein a slot 27a, 27b to slidably dispose therein the (FIG. 1) shown in phantom. Here inputloutputtrans- Y1G spheres 26a, 26b which are connected to end mission line section 30'is used to provide reduced portions of dielectric rods 28a, 28b as shown. Final direct coupling of r.f. energy fed on input line 33a'to precise adjustments of the Y1G spheres about the axis output 1 ine 33b'. Such direct coupling may occu r for 100 may be made with this structure.

certain applications of the embodiment shown in Referring nowto FIG. 7, an alternate embodiment of FIGS. 1-3. Whetherthis coupling is tolerable is a magnetically tuned resonant circuit 9as shown to dependent upon the amount of coupling in compari- include a pair of substrates 31,31'here replacing the son to the system requirements. The distance be- inputloutputsubstrate 30 of the prior embodiments 9, tween the lines 33a, 33b, the frequency of the energy 105 9', 9% as shown. Each substrate 31,31'hasformed fedthereto and the power level are some factors thereon a ground plane conductor34a, 34b and has which will influence direct coupling between lines 33a, formed therefrom a corresponding one of such input 33b. Therefore, the second embodiment 9'is shown or output CPWtransmission lines 33a, 33b. Such which provides reduced direct coupling. This is substrates arejoined with pairs of dielectric spacers accomplished by having such lines diverge atterminal 110 20a, 20b as shown. When joined with the dielectric portions 39a, 39b thereof, as shown, to thereby spacers 20a, 20b, a channel 40 is provided therebe increasethe distance between such lines and thus tween, such channel 40 is here provided to slide reducing coupling of a voltage induced between such therein a conductive slab 42'such thatthe input line lines in accordancewith lld 2 where d is the distance 33a is isolated from the output line 33b and the Y1G separating such lines. Such direct coupling is further 115 spheres 24a, 24b are isolated from the output line (not reduced by making innermost slots 41 a', 41 b'narrow- shown) of substrate 31,31'may be plated and formed er in width wathan the widths Wb of outer slots 41 a, integrally with the ground plane conductors 34a, 34b 41 b. As shown in FIG. 4,direct coupling may occur to insure continuity ofthe slab 42 with the ground when an input signal, for example, propagates on planes34a,34b.

input line 33a and a voltage is induced in strip 120 Referring nowto FIG. 8,the magnetically tuned conductor36b ofoutput line33b, because some ofthe resonantcircuit 9 is shown disposed in a housing 70, magneticflux lines (representing the propagation here of brass. Connected to such housing 70 are a pair magneticfield component ofthe input signal) extend ofcoaxial transmission line connectors 72a, 72b outwardly in the vicinity ofthe outputstrip conductor having center conductors 73a, 73b dielectrically 36b. Due to the nature of CPWtransmission line 125 spaced from outer conductors 73a', 731Y. The center propagation, a difference in magnetic flux which conductors are connected to the stripconductor passes through each one ofsuch gaps in the portions 36a, 36b, and the outer conductors 73a', M' metallization induces a voltage in such output line 33b are connected to the housing 70to provide inputand proportional to such difference. That is, sincethe flux output connections to the magnetically tuned re- in each gap will induce a voltage in the strip conductor, 130 sonantcircuit9.

GB 2 131 628 A 6 with each one of such voltages 180'out of phase with each other, the net currentflowing in such strip conductorwill be the difference between the individual components of such current. Thus, if the gaps are equally wide, coupling will occur becausethe magnetic flux will decreasewith increasing distance andthe distant or outmost slot will have relativelylow amounts of flux therethroug h thanthe innerslot, and the netcurrentwill not bezero.The reducedwidth of inner slot41 a', 41 b'results in reduced direct coupling if equal currentswill bezero and no energy will becoupled into the output strip conductor36b from the input strip conductor 36a. With the magneticallytuned resonant circuit 9' (FIG. 5)the innersiotis made sufficiently narrow (or conversely the outerslot is made sufficiently wide) so asto reducethe amount of magnetic flux therein to be substantially equal to the magneticflux in the outerslot,the difference in suchfluxwill be substantially zero and substantial isolation between input and output lines 33a', 33b will be obtained.

7 GB 2 131 628 A 7 Referring nowto FIGS. 9, 10Jabrication of afour channel dual stagefilter 80 will be briefly described. Onechannel Aof thefourchannel dual stagefilter80 is shownto include a first triangular shaped CM transmission line section 82a', a second triangular shaped ^transmission linesection 82a',spacers 84,84a',Y1G spheres 85a, 85a'and interstage section 83a disposed in a slot87a of a housing 81. Such CPW sections are fabricated in a similarmanneras de- scribed in conjunction with FIGS. 1-3. Coaxial lines 88a, 88a'having center conductors 89a, 89a'are connected to the first and second lines 82a, 82a'as described in conjunction with FIG. 8. In a like manner, each one of the remaining slots 89b-89d of housing 81 has disposed therein a similarset of such CPW transmission line sections 82b-82d, 83b, M', and spacers 84a, 84a'providing in combination additional channels B-D. With the above structure a relatively compact multi-channel filter is provided.

Referring nowto FIGS. 11 -13, a magnetically tuned resonant circuit 109, here a bandpass filter, having improved resonantcircuit characteristics fabricated in accordancewith theteachings of the present inven tion is shown.

Referring first to FIG. 11, the magnetically tuned resonant circuit 109 is shown in the presence of a DC magnetic field intensity HDC, generated by means, not shown. The magnetical ly tuned resonanteircuit 109 includes a first, here input, microstrip transmission line section 110 having a dielectric substrate 112 separating a g round plane conductor 118 and a strip conductor 114. The strip conductor 114 has a f irst portion 11 4a of an arbitrary length and a second portion 11 4b. Strip conductor portions 11 4a and 1 14b are connected together by a pair of outwardly bowed 100 spaced strip conductors 114c', 1 14c% here of equal arc lengths, I., as shown. Outward bowed spaced strip conductors 114c', 11 4c" here provide a planar input r.f. coupling circuit 117 (it isto be noted thatthe strip conductors 11 4c', 1 14c" are spaced a distance d). 105 In orderto strongly couplethe magneticfield component of an r.f. energy signal fed to coupling circuit 117, an effective r.f. short circuit is provided at midpoint 117% 117' thereof. To provide such short circuitthe length of strip conductor portion 11 4b lb is chosen to provide, in combination with a portion of the arc length of either one of strip conductors 11 4c', 11 4c"to the midpoint 117% 117" of the coupling circuit 117, a length 1 = lb + %/2) substantially equal to one quarter of a wavelength (M4) where A is the wavelength of the midband frequency component of the resonant circuit. Further, portion 1 14b of strip conductor 114 has a plurality of spaced strip conduc tor segments 1 14b', 1 14b" formed adjacent thereto.

The spaced strip conductor segments 11 4b', 1 14b" are 120 used to extend the length of the strip conductor portion 11 4b for lower frequency applications by selectively bonding one or more of such segments 1 14b', 1 14b--- together and to the strip conductor portion 114b by conductors (not shown) to thereby provide the requisite length 1 = A14. Strip conductor portion 11 4b is here terminated in an open circuit at the segment end 115 thereof to provide, atthe midpoints 117% 117' respectively of the coupling circuit 117, an effective short circuit to such r.f. energy,130 as is known in the art, since the separation between the open circuit end 115 and the midpoint of the coupling circuit is a quarter of a wavelength. A short circuit is thus created atthe midpoint 117, 117' of each one of the spaced conductors 114a', 114" of the coupling circuit 117. The impedance of a stub 119 (such stub being formed from the strip conductor 114bAhe dielectric 112 and ground plane 118) is selected to provide the resonant circuit 109 with a desired bandwidth. As is known in the art, the impedance Z 110 of such a microstrip transmission line section 110 atthe midpoint 1 17'is related. to the characteristic impedance (-Z.) of the stub 119, operating wavelength Aand length laof such a stub 119 by Z 110 q -jZ. contangent (21rla/A). Thus, the lower the characteristic impedance Z-.the broader the operating bandwidth since there will be a wider range of wavelengths forwhich Z110 will be substantially equal to zero (appear as a short circuit) and thus strongly couple the magnetic field component of such signal in a mannerto be described.

Acircular aperture 116 is bored through the substrata 112 and ground plane conductor 118, symmetrically between the spaced strip conductor portions 11 4c', 114c". A circularvoid 11 8'isformed in the portion of the ground plane 118 using conventional masking and etching techniques, exposing an underlying portion of the substrate 112. The void 118' and the aperture 116 are here concentric. Here the void 11 8'exposes a portion of the substrate 112 extended beyond the periphery of the strip conductors 114c', 114c--- whereasthe aperture 116 is here substantially confined to the region between such strip conductors 114c', 114c% as shown more clearly in FIG. 13, and to be described in more detail hereinafter.

The width (w) of the strip conductor 114a, and the thickness (h) and dielectric constant of the substrate 112 are chosen to provide in combination with the ground plane 118the microstrip transmission line section 110 having a predetermined characteristic impedance-Z., here equal to 50 ohms.Thewidth w'of spaced conductors 114c', 114c--- is chosento provide such lineswith a characteristic impedanceZ, here approximately equal to 100 ohms, with the parallel combination of such pair of lines here providing an impedance of approximately 50 ohms. The characteristic impedance of such transmission line formed from the strip conductors 11 4e', 1 14c--- is here related tothe width of such lines w', the distance of such lines from the ground plane conductor 118 and the thickness and dielectric constant of the substrate. Since a void 11 8'is formed in the ground plane conductor 118, immediately underneath the strip conductors 1 14c', 11 4c-, a transmission line of a predetermined characteristic impedance is provided in part by means of fringe capacitance existing between the ground plane 118 and strip conductors 114c', 1 14c". The size of the void 11 8'in the ground plane 118 is selected to insure thatthe strip conductor portions 11 4a, 1 14b provide, in combination with such ground plane 118 and dielectric 112, transmission lines having predetermined characteristic impedances as described above, and the size of the void 11 8'is also selected such that the ground plane 118 does not significantly interfere 8 with coupling of r.fi. si-iegy as will be described.

Further, the thickness of all sirip conductors are chosen to minimize series resistance and inductance, as would be provided by a thin conducior.

The magnetically tuned resonantcircuit 109 also includes a sphere 138 ofla ferrimagnetic material, here yttrrium iron garnet, and a second, here output, microstrip transmission line section 120 having a strip conductor portion 124 orthogonally spaced from strip conductor portion 114 of thefirst micorstrip transmis- 75 sion line. The second microstrip transmission line also includess a dielectric substrate 122, here separating the second strip conductor 124 and a second ground plane conductor 128, as shown. Strip conductor 124 includes a first portion 124a of an arbitrary length and 80 a second portion 124b. Strip conductor portions 124a and 124b are connected together by a pair of spaced strip conductor portions 124c', 124C, as shown.

Spaced, strip conductors 124c', 124C here provide a planar output r.f. coupling circuit 127. In a similar manner, as previously described, the length of portion 124b is chosen to provide in combination with a portion of strip conductors 124c', 124c--- to midpoints 127% 127---thereof a length, 1, substantially equal to one-quarter of a wavelength (A14). Further, end portion 124b has strip conductor segments 124W, 124W' used to extend the length of the strip conductor portion 124b for lowerfrequency applications, as described above, and the strip conductor portion 124b is hereterminated atthe segmentterminus thereof in 95 an open circuitto provide atthe midpoint 127% 127---of strip conductors 124c',l 24c-, a shortcircuitto re sonantfrequency r.f. energy. Provided between such split strip conductor portions 124c', 124c--- of coupling circuit 127 is an aperture 126 through the dielectric substrate 122. The ground plane conductor 128 is lormed on the surface of the dielectric substrate 122 opposite the strip conductor 124to provide in combination therewith the microstrip transmission line section 120, as shown. Avoid 12Win the ground 105 plane 28 is provided, exposing an underlying portion of the substrate 122. In the same manner as described above, the substrate thickness (h), dielectric constant thereof, and the strip conductor 124width (w) are chosen to provide the microstrip transmission line 110 sec-Lion 120 with a predetermined characteristic impe dance, here equal to 50 ohms. In a similar manner, the width of each planar strip conductor 124c', 124c" is chosen to provide each one ofsuch lines with a 100 ohm characteristic impedance, as previously de scribed. In a preferred embodiment of the invention, microstrip transmission lines 110 and 120 are con structed to be identical in mechanical and electrical characteristics.

As shown more clearly in FIG. 12, the transmission 120 line sections 110 and 120 are joined together to provide a composite transmission line body 130. The transmission lines 110 and 120 are arranged such that the corresponding apertures 116,126 FIG. 11) pro- vided in the respective substrates 112,122 are aligned 125 to provide a common aperture 136 through the joined transmission line sections 110, 120. The transmission line sections 110 and 120 arefurther arranged such that strip conductor portions 114 and 124thereof are spaced from one another by the separation provided GB 2 131628 A 8 bythesubstrates 112 and 122.That is, such microstrip transmission linesections 110, 120 areconnected together along -the suriace of ofthe respective ground planes 110, 128.1o provide a composite ground plans conductor 135, and the exposed areas 112', 122'or are aligned to florm a void 135'in the composite ground plans conductor 135. The strip conductors 111 4 and 124 of each microstrip transmission line section are here orthogonally disposed with respectto each oE ier, as shovin for reasons to be described hereinaller. The sphere 138 of yttrium iron garnet (YIG), is then disposed in the aperture 136, as shown. The aperture 136 provided through the magnetically tuned resonant circuit 109 has a diameter equal to the diameter of the Y1G sphere 138 disposed therein. At one end of the aperture 136 in the magnetically tuned resonant circuit 109 is inserted a button-shaped dielectricYlG sphere support 137 (FIG. 13) upon which the Y1G sphere 138 may have been previously mounted. The sphere support 137 is disposed in the area between coupling circuit 127 and is used to supportthe Y1G sphere 138 in the aperture 136. It is preferable thatthe Y1G sphere 138 be positioned atthe center of the magnetically tuned resonant circuit 109 such thatthe plane (not shown) of the ground plane 135 bisectsthe Y1G sphere 138. Here the Y1G sphere 138 has a diameter 375lim (0.015 inches). The metallization thicknessforthe ground plane 135 is 5pm (0.0002in.) and the thickness of the substrate is 375pm. The diameter of the aperture 136 isthus 37511m in orderto permitthe sphere 138to be disposed therein. The Y1G sphere 138 is preferably orientated priorto insertion within aperture 136 such thatthe external D.C. magnetiefield HDC, provided by disposing the composite body 138 between a rnagnetic pole piece 140a and a flux return Voke 140 (FIG. 13), is disposed with respectto a predetermined crystalographic direction of the VIG sphere 138, such that coupling of a resonance radian freqo Rency energy 0' (herea., ter resonant frequency) is independent of temperature. A preferred apparatus and m el-hod for orientating the Y1G sphere 103 is described in conjunction with FIG. 43 to FIG. 45, al though other methods for orientating a Y1G sphere may be used. The first ends 11 4a, 124a of strip conductors 114,124 are used to couple the mag netically tuned resonant circuit 109 to external components such as a system 160, as shown in FIG. 15. Selection o4],jvhich one of the microstrip transmission lines 110, 120 is used as an input or output line is determined in accorda-iice,,riii-th its connection to the external componems. As previously described, the length of each of such strip conductor portions 114b, 124b is chosento have, in combination with a portion ofithe length ofthe- coupling circuits 117,127, a length 1 substantially equallo a quarter of a wavelength in orderto provide, in combination with the open circuit termination ofisuch lines, an effective r.fK. short circuitatthe midpoints 117, 127ofleach coupling circuit 117, 127, as described above. As is known in the art, a shortcircuit is provided substantially atthe midpoints 117', 127'o'l'the coupling circuits 117,127, respectively, in orderto strongly couplethe magneticfield component of the electromagnetic energyfedtothe input microstrip transmission line section 110 through the Y1G sphere and to the output 9 microwave transmission line section 120. A portion of the input energy having a frequency substantially equa%1 to the resonant frequency co,, of the Y1G sphere 138 is coupled from the input microwave transmission line section 1 10throug h the Y1G sphere 138 to the output microwave transmission line section 120 in a manner to be described. Suffice is hereto say that coupling of such microwave frequency energy having a frequency coi = w. occurs within the reg ion of such spaced strip conductor portions 11 4c', 11 4c% 124c', 124c% respectively.

As shown in FIGS. 13,21 a housing 131 hereof brass is provided to housethe composite transmission line section 130. Such housing includes input and output coaxially connectors 131 a-1 31 a'(FIG. 21) and coaxial to microstrip launchers 131 b-131 b'to couple transmission lines 110, 120to external circuit components.

Referring nowto FIG. 15, a typical system 160which includesthe magnetically tuned resonant circuit 109, here a front end filterfor a radio frequency receiver 168 is shown to include a first transmission line 164 connected between an antenna 162 and the input transmission line 110 of the magnetically tuned resonant circuit 109 and second transmission line 166 connected between the output transmission line section 120 of the magnetically tuned resonantcircuit 109 and the receiver 168. In operation, a radio frequency signal received bythe antenna element 162 is fed to the inputtransmission line 110 of the magnetically tuned resonantcircuit 109,viatransmission lie 164. In accordance with the equation wi = wo, a portion of the microwave signal fedtothe input transmission linesection 110 is coupled to the output transmission linesection 120 of the magnetically tuned resonanteircuit 109 in a mannernowto be described. This coupled signal (notshown) isthen fed to the receiver 168.

Referring nowto FIG. 13 and FIG. 14, a D.C. magnetic field HDc (FIG. 12) is shown with f lux lines thereof normal to the plane of the ground plane conductor 135 105 of the magnetically tuned resonant circuit 109. The DC magnetic field Ht is here generated by placing the magnetically tuned resonant circuit 109 between the pole piece 140a and flux return yoke 140 (FIG. 13), as shown. In the presence of such a DC magnetic field 110

HDc applied along a Z-axis, for example, an input signal is fed to inputtransmission line 110 (FIG. 11) and the signal passes through the spaced, split or bifurcated strip conductor portions 114c', 114c" of input coupling circuit 117 disposed along an X axis, for 115 example, producing an r.f. magneticfield Hrf (FIG. 14) in thevicinity of strip conductor 1 14c', 114c% as shown. In the absence of theY1G sphere 138there is no coupling of the energyfed through the microstrip transmission section 1 10tothe output microwave 120 transmission line 120 sincethe inputcoupling circuit 117 is orthogonally orientated with respectto the outputcoupling circuit 127. Thus, such energy is reflected backtowardsthe inputsource, herethe antenna 162.With aYIG sphere disposed in aperture 136,spaced a distance d along aZ direction thereof, a portion ofthe energyfed onthe inputcoupling circuit 117 is transferred to the Y1G sphere 138.TheY1G sphereis positioned along a direction wheretheX component of r.f. magnetic field Hx has a maximum

GB 2 131 628 A 9 value. Further, duetothe symmetric structure ofthe inputcoupling circuit 117, asshown in FIG. 17,the resultant magnetic field coupling componentHJs relatively uniform through the Y1G sphere 138. Inthe general case,thus,the numberof such strip conductors, their shape, and alignmentwith respecttothe Y1G sphere 138, are selected to provide through the Y1G spherevolume a predetermined magneticfield distribution from a signalfedtosuch strip conductors.

That is, the current fed to such strip conductorsis selecti velychanneled ordistributed amongthe various conductorsto provide a predetermined distribution of the magneticfield generated in response to such current. Generally, in orderto reduce coupling to higher order resonance modes, thefield distribution through a spheroid shaped ferrimagnetic body is chosen to be uniform. Otherfield distributions in combination with differently shaped ferrimagnetic bodies can be provided to insurethat higher order resonance is suppressed. Suppression of higher orderresonance is further described in conjunction with FIGS. 17,17A.

Thefrequency of the energy transferred tothe spins of the electrons in theYIG sphere 138 is related to to, y HDCwherey isthe quantity referred to asthe 11 gyromagnetic ratio- as previously defined. Nonresonantfrequency energy nottransferred to the sphere 138 is reflected backward toward the input source, here the antenna 162. Energytransfer between the input microwave transmission line section 110 and the Y1G sphere 138 thus is possible when the frequency (wi) of the r.f. signal fed thereto is equal to the natural precession frequency w. to the Y1G sphere 138 as defined bythe equation o). = y HDC. When this resonant condition is satisfied (coi = wo), the magnetic field component H,, of the input energyfed to the input coupling circuit 117 having a frequency nearthe resonant frequency (w.) is transferred to the spins of the electrons in the Y1G sphere 138 by making the electrons precess abouttheirZ axis. Precession of electrons abouttheirZ axis produces in response thereto a magnetic moment abouttheY axis, enabling coupling of r. f. energyto output transmission line section 120which is disposed aboutthe Y axis by inducing a voltage in output coupling circuit 127 and providing a currentflow therein. The frequency of such a coupled signal in theY axis circuit is wo, as is well-known inthe art. Further,there is also transferof energy having afrequencywhich deviatesfrom w., the resonant frequency. The strength ofcoupling of energy having afrequencywhich deviatesfrom co. and hence the bandwidth ofthe coupling thereof is determined bythe proximity ofsuch frequencyto (o,, the resonant frequency and impedanceZ,10, Z120 Of thetransmission lines 110, 120 as previously described.

AY1G filter providing a passband off. = 20 MHz at a centerfrequency offo = 10 MHzwheref,, = wj2Ti, tunable over at least 500 MHz band in the X-band range and having an insertion loss atf,, or less than 1.3 db, hasthefollowing properties:

GB 2 131 628 A 10 Symbol DescriDtion W T_ width of strip conductor 114a, 124c width of strip conductor 114cl, 114c'] 124cl, 124cl ws width of stubs 114bf 124b substrate material substrate thickness aperture diameter dielectric constant of substrates 112, 122 D 1 diameter of void d Value 15 mill 3 mill 3 mil I mill alumina mil mil 9.3 mil mil separation of coupling circuit conductors 114cl, 114c I, 124c', 124c--- length of coupling circuit 6.0 mil Referring nowto FIG. 16, the effect of the ground plane conductor 135 of the magnetically tuned resonant circuit 109 on transfer of energy between input and output transmission lines 110, 120 through the Y1G sphere 138 will be described. As is known in the art, when a sphere resonator is in close proximity to a conductive wall, such as the coupling loops orthe filter r.f. housing of the -wire loop type Y1G filter", two principal effectswhich occurare: af requency shift in the resonant frequency (w.) and a 1ine broadening" effect.--- Linebroadening" is aterm in the artwhich refersto an increase inthefrequency bandwhich will resonate with the Y1G sphere 138, albeitata reduced efficiency, thereby increasing the resonant frequency insertion loss of the Y1G sphere 138.

In most prior art structures (not shown) the Y1G sphere 138 is located closeto a conductive wall such asthe coupling loop orthe filter's r.f. housing. In such cases, a frequency shift results from the proximity of the sphereto the conductive wall because the r.f. magneticfield (not shown) associated with the precessing magnetization of electrons in the sphere (the vectorsurn of the precessing magnetization of all the electrons in the sphere) is distorted in the vicinity of the surfacd of the conductive wall due to the conductivity thereof. This distortion of the r.f. magneticfield produces a shift in resonant frequency of the resonant circuit. This shift is partially compensated for in the prior art structure by changing the applied

D.C. field. However, thefrequency shift is also a function of temperature making temperature independant operation more difficuitto achieve. With the present invention, as diagrammatically shown in FIG. 16,the Y1G sphere 138 is disposed midway through the aperture 136. That is,the Y1G sphere 138 is symmetrically disposed through the void 1135'in the ground plane conductor 135. Since, under resonant conditions, the precessing magnetization M in the uniform resonance mode is provided in the Y direction, it is already parallel to the ground plane 138 and hence there is no significant distortion of the magneticfield and thus no significant frequency shift caused bythe ground plane conductor 138.

The second effect provided by close proximity of a sphere resonatorto a conductive su rface is the so-called 1ine broadening" effect which results f rom eddy currents flowing in the conductive wall. The eddy currents resuItfroffl voltages being induced in the conductive wall due to the varying r.f. magnetic field. In the prior art structures mentioned above, the eddy currents and hence the line broadening effect are reduced by positioning the spheres ata greater distance from the conductive wall since the power dissipated due to the -line broadening- effect is proportional to Ild 4 where d is the distance between the conductive wall and the center of the sphere. However, often this approach reduces the coupling between input and output lines and thereby degrades performance. In the present structure, this problem is substantially eliminated because, as shown in FIG. 16, the ground plane conductor 135 bisectsthe Y1G sphere 138. Since a portion of the ground plane conductor 135 can be selectively removed in the area adjacentthe Y1G sphere 138 providing the void 13T, as previously'described, eddy current losses can be minimized. That is, since eddy current loss is related to the distance d between the Y1G sphere 138 and the conductive surface, here the ground plane conductor 135, the diameter of the void 135'through the ground plane conductor 135 can be made sufficiently large without any significant reduction in resonant coupling strength, thereby reducing eddy currents in such ground plane and hence reducing the -line broadening effect- and resonantfrequency insertion loss.

Referring nowto FIG. 17, an idealized graph of the strength of the coupling component Hrf>, (in free space) of the r.f. magneticfield Hrf in the X direction is shown as a function of the vertical distance (i.e. along the axis) between the Y1G sphere 138 and a pairof conductors which approximate the inputcoupling circuit 110 forthe magneticallytuned resonant circuit 109 (curve 1) in comparison with an idealized graph of the coupling component Hrfx as a function of the vertical distance between a single conductorand a Y1G sphere, which approximate a single conductor priorart structure (curve 2). The spatial relationship between the conductors 114,124 (FIG. 12) and the Y1G sphere 138 and a typical prior art structure are diagrammatically shown in FIG. 17. The magnetic field generated by a pair of conductors (in free space) in the region where the Y1G sphere 138 is disposed (curve 1) is relatively uniform throughoutthe Y1G sphere 138 in comparison to the magnetic field generated by a single wire (cu rve 2) thattraverses such region. As is known in the art, Y1G spheres when used in microwave bandpass filtersjor example, due to excitation of nonu niform modes of resonance in the Y1G sphere, will transfer spurious energy signals here shown as peaks 1152a', 11521b'in FIG. 17A (Case 2) having a frequency outside the passband 152'of the filter, as shown. The transfer ofthis spurious energy is generally undesirable. The spurious energy is transferred by exciting higher order modes of ferri- magnetic resonance generally referred to as "magnetostatic modes of resonance!' These modes of resonance occurwhen the Y1G sphere in the presence of the D.C. mag netic field HDC iS positioned where there is a spatial variation of the r.f. magnetic f ield ll(y through the volume of the Y1G sphere 138 such as that shown in FIG. 17 for curve 2. It is theorized here that, as a result of this spatial variation of the field across the Y1G sphere 138, the electrons in the upper half of the sphere oscillate in phase opposition to the electrons in the lower half of the sphere, thus providing phase and amplitude variations of the 1 1 11 GB 2 131628 A 11 resonant energy across the Y1G sphere. Oneof the advantagesof the present invention isthe relative uniformity& the r.f. magnetic field which is provided through theYIG sphere 138, aswas described in conjunction with FIG. 17 (curve 1).The present invention provides a reduced excitation of magnetostatic modes of precession and thus reduced spurious energytransfer (peaks 152a, 152b), as shown in FIG. 17A, case 1, since the magneticfield through the sphere 138 is in general more uniform.

The orientation of the ground plane conductor 135 with respectto the sphere 138 provides an additional advantage overthe above-mentioned prior art structures. As previously described, there is no frequency shiftsincethe r.f. magneticfield associated with the uniform mode of precession is a priori provided in a plane parallel to the ground plane 135 without any distortion in the r.f. magneticfield. For most nonuniform modes, however, the r.f. magnetiefield associ- atedwith the precessing magnetization thereof has components perpenclicularto the ground plane conductor 135. Thus, the resonant frequency of such modes in the presence of a conductive wall is shifted relative to the resonant frequency of the same mode in the absence of a metal wall. Further, in the ground plane will be induced eddy currents from the magnetostatic resonant energywhich will further decrease the strength of spurious energy transmission due to the line broadening effects described earlier. In other words,the coupling circuits 117,127 provide a relatively uniform r.f. excitation of the Y1G sphere 138, resulting in reduced magnetostatic resonance and hence lowerspurious energytransfer. Atthe same time, dueto the line broadening effect on the magnetostatic resonant frequency, the coupling circuits 117,127 provide a significant insertion loss to any nonuniform resonant energy transferred, further reducing spurious responses.

Referring nowto FIGS. 18-20, a two stage magneti- callytuned resonantcircuit 190fabricated according to the teachings of the present invention is shown. Referring firstto FIG. 18,the magnetically tuned resonantcircuit 190 isshownto includea firstinput transmission linesection 110, here substantially identicaltothe input transmission line section 110 described in conjunctionwith FIG. 11, afirstoutput transmission line section 120 substantially identical to the output tra nsm ission linesection 120 described in conjunction with FIG. 11, an interstagetransmis- sion line section 180, and Y1G spheres 198a, 198b, as shown. Interstage transmission line section 180 here includes a dielectric substrate 182 separating a strip conductor 184 and a group plane conductor 188, as shown. The strip conductor 184 is provided substan- tially across the entire length of the substrate 182 (having a length, 11, equal to (2n+ 1) A/4wavelengths (where (2n+l) is an odd multiple multiplier, n is an integer) and includes a pair of quarter wavelength stubs 184a, 184e,two pairs of spaced or bifurcated strip conductor segments 184W, 184b-, and 184d', 184d" providing interstage coupling circuits 185a, 185b and a strip conductor 184c coupling together such segments 184W, 184W' and 184d', 1184d% as shown. Stub portions 184a, 184e have a length, 1, in combination with a portion of the coupling circuits 185a, 185b to provide a quarter wavelength stub as previously described in conjunction with FIGS. 11-13. Provided in the substrate 182 between each pair of such split strip conductors 184W, 184W' and 184d', 184d" is a corresponding aperture 186a, 186b, respectively, through such substrate 182 and ground plane conductor 188, as shown. A pair of circular voids 188a, 188b are formed in the ground plane conductor 188 in the area adjacent such apertures :75 186a, 186b exposing portions of the substrate 182 and the apertures 186a, 186b therein, as described in conjunction with FIG. 11. The distance 12 between the centers of such apertures 186a, 186b is an odd multiple (2n+ 1) of a quarter wavelength A/4where n is an integer. The length, 1, of the strip conductor 184 and the distance 12 between the apertures 186a, 186b are chosen to be an odd multiple of a quarter wavelength in orderto preservethe r.f. short circuits atthe center of each aperture 186a, 186b, as previously described, and to maintain a uniform balance of electrical characteristics across such strip conductor 184. Further, the impedance here approx imately 50 is shown to provide desired coupling between the stages. 1 As shown more clearly in FIGS. 19,20, the input transmission line section 110, the outputtransmission line section 120, and the interstage transmission line section 180 arejoined togetherto provide a composite transmission line body 193. The transmis- sion line sections 110, 120 and 180 are joined together providing a composite ground plane 195. Achannel 191 is obtained between such microwave transmission line sections 110, 120 when such sections 110, 120 arejoined with the interstage transmission line section 180. A suitable housing 131'(FIG. 20) similar to the housing 131 shown in FIG. 21 forthe single stage circuit 109) is provided to hold such transmission line sections 110, 120,180 together. A conductive slab 192 is provided in the channel 191 between such transmission line sections 110, 120. Conductive slab 192 here provides a conductive path to the ground plane 195 between input transmission line section 110 and output tra nsm ission line section 120 to prevent direct coupling of signals therebetween. A pair of apertures 196a, 196b through the dual stage magnetically tuned resonator 190 are provided from apertures 11 6,186a and 126,186b, as previously described in conjunction with FIG. 12, for aperture 136. Each aperture has associated therewith a void 195a, 195b in the ground plane 195 as previously described in conjunction with FIG. 12. As shown in FIG. 20, a first stage 190'of the dual stage magnetically tuned resonant circuit 190 is shown to include a Y1G sphere 198a disposed in aperture 196a, and a second stage 19V of the resonant circuit 190 is shown to include a Y1G sphere 198b disposed in aperture 196b.

Coupling of a portion of an r.f. signal fed to the strip conductor 114 of input transmission line 110 to the strip conductor 124 of output transmission line 120 will now be described. As shown, the external D.C. magneticfield H1)c is here applied normal tothe surface of the composite body 193. The DC magnetic field HDc is generated, as previously described, by placing the magnetical iy tuned resonant circuit between a magnetic pole piece here 140a'and a flux 12 GB 2131 628 A 12 return yoke 140'(FIG. 20). Radio frequency energy in the presence of the DC magnetic field HE)c is fed to strip conductor 114 at portion 114a thereof of the first stage 190'. In accordance with the equation w. =

VHDC, the portion of such input energy having a frequency substantially equal tow. is transferred to the spins of the electrons in Y1G sphere 198a, disposed in aperture 196a, in a similar manner as previously described in conjunction with FIG. 7, by making the electron spins thereof precess aboutthe direction of the external field HDc, herethe-Z-axis. In a like manner, as previously described in conjunction with FIG. 19, the precession of electrons aboutthe-Z axis produces an R.F. magnetic moment in the Y direction, enabling coupling of such energyto the first pair of split strip conductors 184b', 1184b--- of the interstage strip conductor 184. Such coupled energy is then fed along the intermediate strip conductor 184cto the second pair of split strip conductors 184d', 184C. In a similar manner, as described above, substantially all of the energyfed to split strip conductors 1184d'll 84C is transferred to the spins of the electrons in the Y1G sphere 198b and, in a similar manner as described above, such energy is then coupled to the strip conductor 124 and fed tothe output portion 124a thereof.

Suppression of magnetostatic resonance modes, line broadening andfrequency shift effects as described in conjunction with FIGS. 16-17, 17Aforthe single stage magnetically tuned resonant circuit 130 in a like manner appliesthe dual-stage magnetically tuned resonant circuit 190. Since in each single stage 190% 19W' of the dual-stage magnetically tuned resonant circuit 190 the magnetostatic resonance modes are suppressed,the clual-stageffiter may be designed using two pure crystal Y1G spheres. Further,. the dual resonator 190 will have lower insertion loss and enhanced temperature performance dueto reduction or elimination of line broadening and frequency shift effects, as described above forthe magnetically tuned resonator 130.

Alternatively, the couplin circuits shown in FIGS. 11-13 and 18-20 may be provided by a pairof conductivewires coupling such portions of thestrip conductors together, or by a pairof, straight lengths of conductive wires of strip conductors formed on the substrate or byfour conductors properly disposedfor providing a predetermined magneticfield distribution. In addition, such coupling circuits may be directly terminated to ground through a hole drilled or boredthrough the substrates and connected with the ground planeto provide electrical contact. Further,the coupling structure and the mechanical configuration of the magneticallytuned resonant circuit disclosed herein may be usedwith othertypes of mag netical ly tuned resonant circuits such as oscillators and the like.

Referring nowto FIGS. 22-24, fabrication of a magnetically tuned resonantcircuit 209, here a bandpassfilter, having a pulsefield coil integrally formed therewith in accordancewith theteachings of the present invention will be described. Referring first to FIG. 22, a first, here input, microstrip transmission line section 210 is shown to fficlude a dielectric substrate 212 separating aground plane conductor 218 and a strip conductor 214. The strip conductor 214 has a first portion 214a of an arbitrary length and a second portion 214b. Strip conductnr portion 214a is split crosswise providing portions 2114a', 214" there- of with a channel 214a... therebetween, as shown. Strip conductor portions 214a'and 214a" are electrically connected together by a lowfrequency blocking capacitor219.

As shown in FIG. 22A, blocking capacitor 219 has a first conductive plate 219a connected to portion 214a' and a second conductive plate 219b connected to portion 214% via a conductive interconnect 219c which bridgesthe channel 214a---.The plates 219a, 219b are spaced apart by a dielectricsiab 219d. The value of capacitancefor capacitor219 is chosento provide a very low impeclanceto radio frequency electromagnetic energy and a relatively high impedanceto lowerfrequency electromagnetic energy,to isolate such energyfrom the input portion 214a'of the strip conductor 214.

As further shown in FIG. 22, the strip conductor 214 includes a second strip conductor portion 214b. Strip conductor portions 214a--- and 214b are connected together by a pair of spaced strip conductors 214c', 2114c% here providing a planar input r.f. coupling circuit 217. The length of strip conductor portion 214b is chosen to provide, in combination with a portion of the length of strip conductors 214c, 2114c-- - to midpoints 217% 217---of the coupling circuit, a length, 1, substantially equal to one quarterof a wavelength (A14). Further, portion 214b of strip conductor 214 has a plurality of strip conductor segments 214d', 214d--formed adjacent thereto, used to extend the length of the strip conductor portion 214b for lowerfrequency applications and hence longer wavelengths byselectively bonding one or more of such segments to the strip conductor portion 214b. Strip conductor portion 214b is hereterminated in an open circuit atthe segment end thereofto provide atthe midpoints 217% 2117" of the coupling circuit 217, a short circuitto such r.f. energy, as previously described in conjunction with FIG. 11. Further, the impedance of a stub219 (such stub 219 being formed from the strip conductor 214b,the dielectric 212 and ground plane 218) is selected to providethe resonant circuit with the desired bandwidth, as previously described in conjunction with FIG. 11 for stub 119.

Portion 214b and segments 214d', 214C thereof are split or etched lengthwise, to provide strip conductor portion 214b a first bifurcated portion 214Wand a second bifurcated portion 214W' spaced by a channel 214b"', as shown. The width of such channel is selected to provide isolation between such conductor portions 214b', 2114W' for lowfrequency signals butto provide effectively a single conductor 214b due to fringe capacitance between such conductor portions 214b', 2114W' for radiofrequency signals. The microstrip transmission line section 210 further includes a first centertapped half wavelength (A12) strip conductor stub 21 Vintegrallyformed at a first end with the bifurcated portion 214b', andterminated in an open circuit at a second end. The center of such stub 21 Vis connected to an input currentfeed line 215a. A second A/2 centertapped strip conductor stub 21 V is shown integrally formed at a first end with the 13 GB 2 131 628 A 13 0 split portion 2114W' and terminated at a second end in an open circuit (0). The center of the stub 211-- provides a second terminal to provide a return flow path forthe signal fed to currentfeed line 215a. Strip conductor stubs 21 V, 21 V are here provided to block flow of r.f. energy through a current pulse source (FIG. 38). Each stub 21 V, 2111% as previously de scribed, is provided with a length equal to A12.

As previously described, an open circuit at a first end of a transmission line will provide at a second end thereof, an effective r.f. short circuit, if the distance separating such ends is a quarter of a wavelength, for signals having a quarter wavelength substantially equal to the length of such transmission lines. Similarly, an effective r.f. short circuit at a f irst end of a transmission line will provide at a second end thereof an effective r.f. open circuit, If the distance separating such ends is a quarter of a wavelength. Here by providing an open circuit at the ends of each stub 211% 211 " respectively, an effective 85 r.f. short circuit is provided atthe center taps of each stub, and thus at the ends connectedto split conductors 214W, 214V an effective r.f. open circuit (o) is provided since one quarter of a wavelength therefrom at each centertap there is an effective r.f.

short circuit.Thus, the stubs 21 V, 211---isolate r.f.

energyfed to strip conductor 214b, by providing open circuitsto such r.f. energywhile feeding a current pulseto the coupling circuit 217to produce a magneticfield in response thereto, in a mannerto be described.

Provided through the substrate 212 and ground plane conductor218 between the planar, spaced strip conductor portions 214c', 214c" is an aperture 216.

The ground plane conductor 218 is formed on the surface of the dielectric substrate 212 opposite the strip conductor 214to provide in combination with such strip conductor 214 and dielectric substrate 212 the microstrip transmission line section 210, as shown. A void 218'isformed in the ground plane 218 using conventional masking and etching techniques, exposing a portion of the underlying substrate 212.

The void 21Win the ground plane 218 is concentrical ly spaced aboutthe aperture 216 and exposes portions of the substrate 212 extended beyond the periphery of the strip conductors 214c', 214c---. As previously described, the width (w) of the strip conductor 214, and the thickness (h) and dielectric constant of the substrate 212 are chosen to provide in combination with the g rou nd plane 218 the micros trip transmission line section 210 with a predeter mined characteristic impeclanceZ, here equal to 50 ohms and thewidth Wof planarspaced conductors 214c', 214c" is chosen to provide such lineswith a characteristic impedance Z-., here approximately equal to 100 ohms, with parallel combination of such lines here providing an impedance of approximately ohms. Thethickness of each one of such conduc tors 214e, 214c--- is chosen to minimize series resistance and inductance, as would be provided by a thin conductor.

The magnetically tuned resonant circuit 209 also includesthe second, here output, microstrip trans mission line section 120 as was previously described in conjunction with FIG. 11, and a Y1G sphere 238.

As shown more clearly in FIG. 23, the microstrip transmission line section 210 and the microstrip transmission line section 120 are joined togetherto provide a composite transmission line body 230. A single turn pulse field coil 239 for changing the strength of the D.C. magneticfield in the area adjacentthe Y1G sphere 238, is here provided bythe A14 portion 211 a'of stub 21 Yconnected to conductor portion 214b', the planar spaced conductors 214c',

214c% the conductor portion 214W' and the A14 portion 211 a" of stub 211 " connected to conductor portion 214b---. The strength of the field is changed in a mannerto be described in conjunction with FIGS. 24-25. It isto be noted that the transmission line sections 210 and 120 are arranged in a manneras describedin conjunction with FIGS. 24to 25.

Referring nowto FIG. 38,39, a driver circuit 410 (FIG. 38)for providing, in responseto a control signal 11 pulse on- (FIG. 39), a pulsesignal to currentfeed line 215a will be described. Driver circuit 410 here includesa transmission line 412 connected between a voltage source416 and a switching element414, here connected tothe gate electrocle414a of a field effect transistor (FET). (Here a "HEXFE7' manufactured by

International Rectifier Part Number IRF 221 is used). Shunt mounted between ground and the gate electrode 414a is a termination resistor RT provided to match the impedance of thetransmission line 412 to that of the input im pedance of the FET 414. The drain electrode 414b of FET 414 is connected to a power source +V, filter by capacitors 421 a, 421 b to provide the current pulse, and the source 414c electrode is connected to the currentfeed line 215a, as shown. In response to the "pulse onsignal, a voltage level of here + 10.0 volts is applied to the gate electrode 414 to turn the FET 414 "on" and to permit cu rrentto f low from the power supply 418, the cu rrent feed line 215a and through the coil 239 to g round, as shown in FIG. 39. A voltage level of here zero volts is applied to tu rn the driver circuit off.

Referring now to FIG. 26, a typical application 260 of the magnetically tuned resonant circuit 209, here a f ront end f ilter for a radio frequency receiver 268 is shown to include a first transmission line 264 connected between a duplexer 261 and the input transmission line 210 of the magneticallytuned resonant circuit 209 and second transmission line 266 connected between the output tra nsm ission line section 220 of the magnetically tuned resonant circuit 209 and the receiver 268. The du plexer 261, here an r.f. switch is also connected to a transmitter 263 and an antenna 262. In operation, the transmitter 263 sends out a very hig h power pulse of microwave energy atthe resonant frequency co.. The duplexer 261 switches the signal such that most of the energy of the transmitted signal is fed to the antenna 262. However, a portion of the signal leaks through the duplexer to the received path. In a fi rst mode of the operation,the resonant frequency of such circuit209 is shifted by changing the magnitude of the DC magneticfield HDr- in a mannerto be described and such energy is prevented from coupling through the resonant circuit 209 to the receiver 268. After a high power signal transmission and priorto reception of an echo signal, the transmitter switches the duplexer 14 261 to connectthe antenna 262 to the receiver 268, and the echo signal is fed to the receiver 268th rough the magneticallytuned resonant circuit 209 in a mannerto be described.

Referring now to FIG. 24 and FIG. 25, the magneti- 70 callytuned resonantcircuit 209 is shown in the presence of the D.C. magnetic field HDC with flux lines thereof normal to the ground plane 235 of the magnetically tuned resonant circuit 209. The DC magneticfield HDCis heregenerated by placing the magnetically tuned resonant circuit 230 between a magnetic polepiece 240a and aflux return yoke 240 (FIG. 24), as shown. In the presence of such a field HDC applied along a Z axis, for example, an inputsignal is fed to input transmission line 210 (FIG. 22) and the signal passes through the split strip conductor portions 214c', 214c--- of inputcoupling circuit 217 disposed along an X axis, for example, producing an r.f. magneticfield Hrf (FIG. 25) in the vicinity of strip conductor214c', 214c% as shown. Withoutthe Y1G sphere 238 disposed in aperture 236, there is no coupling of the energy fed through the microstrip transmission section 210 to the output microwave transmission line 120 as previously described in conjunction with FIGS. 11 to 13. With a Y1G sphere disposed in aperture 236, a portion ofthe energyfed on the input coupling circuit217 is absorbed bythe Y1G sphere 239 as previously described in conjunction with FIGS. 11 to 13. In the general case,thus, the number ofsuch strip conductors, their shape, and alignment with respect to the Y1G sphere 238, are selected to provide through the Y1G sphere volume a predetermined magneticfield distribution from a signal fedto such strip conductors as previously described in conjunction with FIGS. 11 to 13. However, often it is desirableto preventcoupling of r.f. energy between input section 210 and output section 120 (FIG. 26) through the Y1G sphere 238 such as during transmission by a high power transmitter 263 having a frequency equal to coo, to prevent magnetic saturation ofthe Y1G sphere and potential damageto the receiver 266 during the transmission periodfrom transmitted energythat leaks into the receiver path. In accordance with the invention, a pulse signal is fed to currentfed line 215a (FIG. 22) from driver 410 (FIG. 38) providing a current signal flow (1p) in the strip conductors 214c', 214c--- around the aperture 236 as indicated in FIG. 25. The current in such strip conductors 214c', 214C produces in reponse thereto a magneticfield HDcp around the resonant body. Depending upon the direction of currentflow, such field either aids or opposesthe external D. C. field HDC. In any event, in responseto the combination ofthe pulsed magneticfield HDcp and the external D.C.

magneticfield HDC,the shifted resonant frequency (w.s) ofthe magnetically tuned resonantcircuit 209 is given as co.s = V (HDC HDCP), or in otherwordsthe resonant frequency is changed by an amountequal to yHDcp. Thus, during transmission ofenergy having a frequency(o., in responseto a currentflowthrough the coupling circuit217, the magnetically tuned resonantcircuit 209will isolate such energyfromthe receiver268 since the transmitted frequency CO, thereofwill not equal wos, the shifted resonant frequency, and thus the resonant condition ofabsorp- GB 2 131628 A 14 tion of energywill not besatisfied, and such energy will be reflected backwards toward the duplexer361.

In general,when a pluralityof co-ductors are used to provide a selected r. f. magneticfield distribution, a pulsed currentsignal fedto such conductorswill provide in response thereto, a magneticfield proportional to thetotal current flow therein. The above structure in addition provides all the improvements in the operating characteristics of the magnetically pulsed tuned resonant circuit 219 such as reduced spurious energytransfer due to reduced activation or coupling to nonuniform resonance modes, reduced eddy current line broadening and substantial elimination of frequency shift, as detcribed in conjunction with FIGS. 16,17,17A.

AY1Gfilter providing a passband of f. = 20 MHz wheref. = co./2ri ata centerfrequency off. = 10 GHz, tunable overat least a 500 MHz band intheXband range having an insertion loss atf. of lessthan 1.3 db, and capable of shifting f. by 25 MHz in lessthan 100 nanoseconds using driver410 hasthefollowing properties:

svmhol Description

1 W 1width of strip conductor 214a, 224c Value mil width of strip conductor 214cl, 214cl 3 mil 124cl, 124cl 3 mil nil alumina 2.mil mil mil 9.3 mil mil mil sphere diameter 15 mil Referring nowto FIGS. 27-29, the fabrication of a dual stage magneticallytuned resonant circuit 290 each having a single pulsefield coil integrally formed therein according totheteachings of the invention will be described.

Referring firstto FIG. 27,the magnetically tuned resonant circuit 290 is shown to include a first input transmission line section 110, here substantially identical to the input transmission line section 110 described in conjunction with FIG. 11, a first output transmission line section 120 substantially identical to the output tra nsm ission line section 120 described in conjunction with FIG. 11, an interstagetransmission line section 280, and Y1G spheres 298a, 298b in the presence of magneticfield HE)c, as shown. Interstage transmission line section 280 here includes a dielectric substrate 282 separating a strip conductor 284 and a ground plane conductor 288, as shown. The strip conductor 284 is provided substantially across the entire length of the substrate 282 (having a length, 11, equal to (2n+ 1) A/4wavelengths where (2n+ 1) is an odd multiple multiplier) and includes a pair of quarter wavelength stubs 284a, 284e,two pairs of planar spaced strip conductor segments 284b', 284V, and 284d', 284d--- providing interstage coupling circuits 285a, 285b and corres- 1 1 1 1 1 1 1 1 1 1 width of stubs 214b, 124b 1 substrate material 1 channel width (214b...

1 substrate thickness substrate diameter k dielectric constant of substrates 212, 122 separation of coupling circuit conductors at midpoint 214c', 214c-, 124cl, 124c-- c 1 length of coupling circuit diameter of void k ponding strip conductors 284c', 284c--- coupling together such segments 284W, 284b--- and 284d', 284d", as shown. Stub portions 284a, 284e have a length in combination with a portion of a correspond- ing one of the coupling circuits 285a, 285b to provide a corresponding length, 1, as previously described in conjunction with FIG. 11. Provided in the substrate 282 between each pair of such spaced strip conductors 284W, 284b--- and 284d', 284d" is a corresponding aperture 286a, 286b, respectively, through such substrate 282 and ground plane conductor 288, as shown. Portions of the ground plane conductor 288 in the area adjacentsuch apertures 286a, 286b are removed, exposing portions 282a, 282b of the substrate 282 and the apertures 286a, 286btherein as described in conjunction with FIG. 11. The distance 12 between the centers of such apertures is an odd multiple (2n+ 1) of a qua rter wavelength A14 where n is an integer. Each length, 1, of the strip conductor 284 and portions of the coupling circuits 285a, 285b and the distance 12 between the apertures 286a, 286b are chosen to be an odd multiple of a quarter wavelength in orderto preserve the r.f. short circuits atthe center of each aperture 286a,286b, as previously described, andto maintain a uniform balance of electrical characteristics across such strip conductor284.

The microstrip transmission line 210further includes a first centertapped half wavelength (A12) strip conductor stub 28Vintegrally formed atfirstend with the center of split strip conductor portion 284c'and terminated at a second end in an open circuit (0). The center of such stub 28Vis connected to an input currentfeed line 215a. A second M2 centertapped strip conductor stub 281 " is shown integrally formed at a first end to the split strip conductor 284c--- and terminated at a second end in an open circuit (0). The center of the stub 281 " provides a return path for line 21 5a, as previously described. Strip conductor stubs 281% 281 " are here provided to blockflow of r.f.

energy through the current bias source, as previously described. Here by providing an open circuit atthe ends of each stub 281% 281 % respectively, a short circuitto r.f. energy is provided atthe centertaps of each stub, as previously described, and atthe ends connected to split conductors 285% 28W' an r.f. open circuit (0) to r.f. energy is thus provided since one quarter of a wavelength therefrom at each centertap there is a short circuit. Substantially complete r.f. isolation from the current source is thus provided by this configuration since the interstage transmission line section has coupled thereon only resonant frequency energy having a wavelength corresponding to the length of such stubs as described above.

As shown more clearly in FIG. 28, the Y1G spheres 298a, 298b,the input transmission line section 110, the output transmission line section 120, and the interstage transmission line section 280 are joined togetherto provide a composite transmission line body 293. The transmission line sections 110, 120, 180 arejoined together providing a single ground plane 295, as shown. Achannel 291 is obtained between such microwave transmission line sections 110, 120when such sections 119,120 are disposed on the interstage transmission line section 280. A conductive slab 292 is provided in the channel 291 GB 2 131 628 A is between such transmission line sections 110, 120. Conductive slab 292 here provides a conductive path to the ground plane 295 between input transmission line section 210 and output transmission line section 120to prevent direct coupling of signalstherebetween.A pairof apertures296a, 296bthrough the dual stage magnetically tuned resonator290 are providedfrorn aper-tures216,286a and 226,286b, as previously described in conjunctionwith FIGS. 11-13, foraperture 136. Each aperture has associated therewith avold295a, 295b intheground plane295, as previously described in conjunctionwith FIG. 12. A first stage 290' (FIG. 29) of thedual stage magnetically tuned resonant circuit 290 isshownto includetheY1G sphere 298a disposed in aperture296a, and a second stage290" of the resonant circuit 290 isshownto includetheY1G sphere 298b disposed in aperture 296b.

In afirst modeof operation, a portion of an r.f.

signal fed to the strip conductorl 14of input transmission line 110 iscoupledtothe strip conductor 124of output transmission line 120 in a mannerto bedescribed.The external D.C. magneticfield HDC is applied normaltothe surfaceof the resonator290 with-HDcpthe pulsed magnetic component zero for thefirstmode of operation. Input microwave frequencyenergyisfedto stripconductor 1 14atend portion 114a tothefirst stage 29Win the presenceofthe DC magnetic-field, HDC. In accordance with the equation (o,,=wi,a portion of such inputenergy having a frequency substantially equal to co. istransferredto the spins of the electrons in Y1G sphere 298a, disposed in aperture 296a, as previously described in conjunction with FIGS. 24-25, causing such electron spinsto precess in a direction along the-Z axis (in a direction parallel to the magneticfield HDC) at a frequency co. as is well-known in the art. In a like manner, as previously described in conjunction with FIGS. 24-25, an r.f. magneticfield is produced about the sphere 298a and a magnetic moment of the precession of electrons in the X direction is produced in theY direction, enabling coupling of such energyto the first interstage coupling circuit 285a. Such coupled energy is then fed along such strip conductor 284c to the second interstage coupling circuit 285b. In a similar manner, as described above, substantially all of the energyfed to coupling circuit 285b is transferredto the spins of the electrons in the Y1G sphere 298b and in a similar manner as described above such energy is then coupled to the strip conductor 224 and fed to the output term i nus 224a thereof. Suppression of magnetostatic resonance modes, line broadening and frequency shift effects as described in conjunction with FIGS. 16,17,17Aforthe single stage resonator 109 in a like manner applies to the magnetically tuned resonant circuit 290. Since in each single stage 290', 29W of the dual-stage magneticallytuned resonator290the magnetostatic resonance modes are surpressed, the dual-stage filter may be designed using two pure crystal Y1G spheres. Further,the dual resonator 290 will have lower insertion loss and enhanced temperature performance dueto reduction orelimination of line broadening and frequencyshift effects, as described above for the magnetically tuned resonant circuit 16 GB 2 131628 A 16 209 In a second mode of operation, r.f. energy is fed to transmission line section 210, but the magnetic f ields around the spheres 298a, 298b are modified by pulsed DC magnetic fields HDCp to change the 70 resonant frequency of the Y1G spheres 298a, 298b and hence preventcoupling of energyto outputtransmis sion fine section 220. In this mannerthe magnetically tuned resonantcircuit is detuned for r.f. energy of a frequency co. and thus reflects such energy back towardsthe source and provides protection to the receiver 268. Priorto the time of arrival of such r.f.

energy a voltage pulse signal is fed to the driver circuit 410 (FIG. 38) to provide a current pulse on line 215a which is synchronized to theflow of such r.f.

energy, as shown in FIG. 39. A currentflowfrom current line 215a in two paths around the Y1G spheres 298a, 298b is provided. Afirst path denoted by solid arrows is provided around a single turn coil 297 formed by stub 281', stripconductor portions 284c', 284W,284", 284c"and stub 2811" providing In response to such currentflow a pulsed d.c. magneticfield HDCp having an orientation normal to the surface of the magnetically tuned resonant circuit 290 and a direc tion upward, as shown in FIG. 14. A second path is provided around a coil 297'formed by stub 281'strip conductor portion 284c', 284d', 28W' and stub 2811" providing in responseto such currentflow a pulsed d.c. magnetic HDCpb having an orientation normal to the surface of the magneticallytuned resonant circuit 290 and a direction downward, as shown in FIG. 14.

Thus, in the presence of an externally applied d.c.

magneticfield HDC, the pulsed fields HDca and HDCb either aid or oppose the field HDC, thus shifting the resonance frequency of each resonator accordingly.

For resonator A, the shifted resonant frequency WoAs is given by WoAs =y(HDC HDcpa) and for resonator B the shifted resonantfrequency is given as C0oBs y(HDC HDCpb).

Referring nowto FIG. 31,32 and 33, alternate configurations for selectively shifting the resonant frequencies of the magnetically tuned resonators are shown. An interstage transmission line 280 shown in FIG. 27 is configured bysplitting the strip conductor portion 284a and the strip conductor portion 284cto provide a single current loop here around here around the Y1G sphere 298b tofrequency shiftthe resonance frequency of stage 290". No current path is provided around resonatorA, since stub 284a was split length-wiseto prevent coupling to a return path.

There is no frequency sliift of the resonant frequency of Y1G sphere 298a. In FIGS. 32,33 are shown alternate interstage transmission line sections 280", 28Cprovided to shiftYIG sphere 298a and Y1G sphere 298b in the same direction by providing a current path around each one of the resonators and having a current in each path flowing in the same direction around such resonators using a pair of such driver circuits 410 (FIG. 32). In addition as shown in FIG. 33, stub portions 281 a, 281 b have A14 portions which are here connected directlyto ground to provide an effective r.f. open circuit atthe respective coupling circuits, as is known in the art.

Referring nowto FIGS. 34,35,36 and 37 an alternate embodiment of a frequency stepped mag- netical ly tuned resonant circuit 309 here a bandpass filterwill be described.

Referring firstto FIG. 34, a coupling circuit section 310 isshown to include a dielectric substrate 311 supporting a firststrip conductor 314 which is connected to a corresponding quarter wavelength stub 314a, via a thinner portion 314'of strip conductor 314 and a second strip conductor 316 which is connected to a corresponding quarter wavelength stub 316a, via a thinner portion 316'of strip conductor 316 and a conductor 317 which crosses or bridges over conductor 314'and is dielectrically spaced therefrom. Here a bonding wire is shown as conductor 317, but a plated overlay as known in the art may alternatively be used. On a surface of substrate 311 oppositethe surface supporting the strip conductors 312,314 is provided a ground plane conductor318. A void 318'is provided in the ground plane conductor 318 exposing an underlying portion of the dielectric substrate311.

The magnetically tuned resonant circuit309 also includes a Y1G sphere 338 and a coil section 320 having a substrate 321 supporting a pair of strip conductors 322,324 and a spiral coil 326. Such a pair of strip conductors 322,324 are provided to make electrical contactto the coil 326, and to provide means to couple thereto a current source such as the circuit 410 described in conjunction with FIG. 38. An aperture 329 is provided in the substrate 321 for disposing therein the Y1G sphere 338. The Y1G sphere 338 is here held in aperture 329 by a suitable low loss epoxy.

As shown more clearly in FIG. 35,the transmission line section 310 and coil section 320 are joined together, providing a composite body330 and such thatthe ground plane conductor318 is intermediate the strip conductors 314,316 and the coil 320. The transmission line section 310 and the coil section 320 are further mounted such that the aperture 329 formed in the substrate 321 is concentrically aligned with the void 31Win ground plane 318. As shown, the Y1G sphere 338 is here exposed in aperture 329. Here in orderto provide maximum pulsed magneticfield intensity, the Y1G sphere 338 is disposed in aperture

329 such thatthe coil 326 is symmetrically disposed about the Y1G sphere 338. In a first mode of operation, r.f. energy is coupled between such coupling circuits through the Y1G sphere 338, in a manner as previously described. In a second mode of operation, a current pulse signal here fed from driver31 0 (FIG. 38) isfed to one of such strip conductor lines such as 322with line 324 providing a return path. In response to such currentflow around coil 326 a large pulsed D.C. magneticfield HDCp is provided. Thus, the resonant frequency of the Y1G sphere 338 is shifted in accordance with the equation w. = V (HDC RDcp) and substantial isolation of energy having a frequency w. = yHDC is provided as previously described.The coil 326 (FIG. 22) is here used to rapidly switchthe pulsed D.C. magneticfield HDC on andoff as desired. As shown in FIG. 25 in operation,when thefrequency stepped magneticallytuned resonant circuit309 is located adjacent transmitter 263Jor example, to prevent a portion of thetransmitted high energyfrom being coupled through the frequency stepped mag- 17 netically tuned filer, on transmit, a current signal is here fed to such coil 326 to rapidly switch the d.c. magnetic field HDCp on and hence to change the resonant frequency in accordance with the equation 5 w. = y(HDC HDCp) as previously described. Since a cu rrent pulse is being fed through a coil 326 here having a relatively low inductance, and which is proximately and concentrically spaced from the Y1G sphere 338,the magneticfield HDCp can be pulsed on or off rapidly in such region thereby permitting the magnetically tuned resonatorto selectively isolate or couple resonant frequency to energyfed to the input transmission line 314. Further, by mounting the coil on the surface of the substrata 320 (FIG. 21), substrate 312 (FIG. 1), or substrata 382 (FIG. 12), the thermal energy generated bypassing a relatively large currentsignal therethrough is dissipated faster, enabling longer pulsed operation and higher pulse dutycycles, of curreritto createthe pulsed magnetic field HDCP. As previously described in conjunction with FIG. 22, r.f. decoupling A12 stubs may be used in conjunction with coil 226 to prevent coupling of r.f. energy coupled to such coil 226.

A Y1G filter providing a passband of f. = 23 MHz where fo = co.12iT, at a center band frequency of fo, = 10 GHz, tu na ble over at least a 500 M Hz band in the X-ba nd range, havi rig a n insertion loss of less than 1 db and ca pa ble of shifting f, by 300 MHz in less th a n 50 nanoseconds using driver 410, has the following characteristics:

svmbol Description

W I Whs k hl D a.

Value 10 mil 2.5 mil 1 mil mil 9.3 1 10 mill i so mill inner diameter of first turn of' coill 326 i 45 mill 1 4 mil width of conductor 314, 316 width of conductor 3141, 3161 width of stub 314ap 316a substrate thickness dielectric constant spacer thickness diameter of void 318 number of turns Referring nowto FIGS. 40,41 and 42, an alternate embodiment of a frequency stepped dual-stage magnetically tuned resonant circuit 390 will be described. Referring firstto FIG. 40, a dual-stage coupling circuitsection 350 is shown to include a dielectric substate 352 separating a ground plane 354 from strip conductors 356a, 356b, 356c, as shown. Strip conductors W0c here includes discrete strip conductors 356c', 356c--- and 356c--- connected together by plated overlays (as known in the art) or by here bonding wires 357,357'. In a similar manner as described in conjunction with FIG. 34, such conductors 356a, 356b, 356c here form a pair of coupling circuits 358,358'. Here sections 356a', 356Wof strip conductors 356a, 356b provide A14 stubs as does sections 35Wand 356c... as described above. Portions 354', 354" of the ground plane conductors 354 are removed exposing underlying portions of the dielectric substrate 352.

The magnetically tuned resonant circuit 320 also includes a pair of coil sections370a, 370b here substantially identical tothe end section 320 preGB 2 131 628 A 17 viously described. Here such coil sections are embedded in a corresponding pair of apertures 382a, 382b provided in a housing 380 bya suitable low loss epoxy. In a similar manner, Y1G spheres386a, 386b are likewise epoxied into apertures384a, 384b provided in coil sections 370a, 370b as previously described. Housing has attached thereto coaxial connectors and launchers 383 and connector384 (to feed current pulses to the coil sections), as shown.

As shown more clearly in FIGS. 41 and 42, the coupling section 350 is disposed in housing 380 as are Y1G apheres 384a, 384b and coil sections 370a, 370b to providethe frequency step magnetically tuned dual-stage filter 390. By providing a current pulse to the coil, here lines 392a, 392b which are connected to the coils 370a, 370b, the magneticfields HDCp, HDCpb are provided to shiftthe resonant frequency of each sphere 386a, 386b as previously described in conjunction with FIGS. 34-36.

Alternatively, the coupling section 310 may include a plurality of conductors, forthe coupling sections 314', 316', to distribute energy fed thereto and hence shape the r.f. magnetic field as previously described. Also, the coil 326 as described above may be, incorporated in the embodiments described in conjunction with FIGS. 1-33.

Referring nowto FIG. 43, an apparatus 510 for orientating a ferrimagnetic sphere along a predetermined crystal log raphic direction includes afirst pair of coils 512,512'here including wire conductors 512a, 512a'wound around plasticcores 512b, 512W. Coils 512,512'are arranged in a corresponding plastic support 516. Coils 512,512'provide a magneticfield %) of here 1000 gauss in a horizontal orY direction, as shown. The apparatus 510 also includes a second pair of coils 522,522'here including wire conductors 522,522a'wound around plastic cores

522b, 522W. Coils 522,522'are arranged on the plastic support 516 and are disposed within the region confined bythefirst pair of coils 512,512'. The axis of such coils 522,522'are disposed at an angle E) of here 70. 53'with respectto the axis of the first pair of coils 512,512', as shown. Coils 522,522'provide a second magnetic H2 of here 1000 gauss. The apparatus further includes a platform 30 centrally disposed between such pairs of coils 512,512', 522,522', as shown. Each pairof coils 512,512', 522,522'are arranged in such a wayasto provide a magneticfield between each of such pair of coils having directions which correspond to a so-called--- easyaxis" of the sphere.

Referring nowto FIGS. 44 and 45, the platform 530 here of lucite is supported by a support rod 532 here of lucite having a first surface 530'here oppositethe support rod 32 disposed at a predetermined direction with respectto the horizontal plane of the apparatus 510. Here the surface is inclined at an angle 0 of 5.59' with respectto the horizontal direction. Athreaded aperture 530a is provided in the platform 530 and a nylon screw 535 is threaded therein. The nylon screw 535 is inserted normal to the horizontal direction and has an upper portion wherein is embedded a watch jewel 534 here of sapphire. Thewatch jewel 534 has a recessed portion 534a to supportthe Y1G sphere 138 (FIG. 13). The nylon screw35 is provided to adjustthe 18 GB 2 131 628 A 18 position of theYIG sphere 138,to accommodatethe apparatus for here a varietyofYIG spheres of various diameters. As shown in FIG. 44, the screw 535 and watchjewel 534have an aperture 539therein for applying asmall negative pressureto holdtheYIG sphere inthe recess 534a. A cover member 536 having an aperture 536'corresponding in size and shape to the Y1G sphere support 37 (FIG. 13) is then fastened with screws 536a and 536b to the platform 530 along the inclined surface portion 530'thereof. The apparatus 510 is here usedto orientate the sphere 138 as follows: a negative pressure is initially applied through aperture 539to insure thatYIG sphere 138 is properly disposed in the recessed portion 534a of watch jewel 534; the negative pressure is then removed; a series of pulses of currentfrom a current means (not shown) a re alternatively applied to each coil of such pairs of coils 512, 512% 522, 522% in tu rn, at intervals of here one pulse every 20 seconds, with such pulse having a pulse width of approximately 100 ms; in response to each pulse of current to each pair of coils 512,512', 522,522'a magnetic field H,, H2 is generated, in turn, between each pair of coils and the Y1G sphere 138 rotates in response to each of such fields tending to align itself such that a pair of coplanar body diagonals of the sphere's crystal logra phic structure are parallel with the directions of the field H,, H2; after approximatelyfive to six minutes of alternate pulsing of each pair of such coils, the Y1G sphere 138 is orientated such thatthe magnetic fields H,, H2 are aligned with one of the---easyaxis- of the sphere's structu re. Temperature invariant orientation of the Y1G sphere 138 is provided when the sphere support 137 is brought into contact with the sphere 138 since the sphere support 137 is brought into contact with the sphere 138 normal to the inclined surface 530'and at the bias ang le 0 with respect to the vertical axis of the sphere (0 is here equal to the incline of the platform surface 30% Thus,the Y1G sphere 138 is orientated about a temperature invariant axiswith respectto the direction of engagement of the Y1G sphere support 137 with the Y1G sphere 138, since the Y1G sphere support 137 engagesthe Y1G sphere at an angle of 5.59'removed from the vertical axis of the sphere 138. Initial alignmentof the sphere 138 so thatthe easy axis of the sphere's crystallographic structure are aligned with the axes of the coils in combination with a calibrated attachment of the sphere support 137 at a predetermined direction with respectto the vertical direction of the initially aligned sphere 138 on the axes of the coils, provides a sphere 138 orientated about a temperature invariant axis. In orderto check orientation, several methods may be used including X-ray diffraction analysis as known in the art, orby testing performance of such sphere in one of the magnetictuned resonant circuits previously described in conjunction with FIGS. 1-42.

Having described preferred embodiments of the invention, itwill now be apparentto one of skill in the archat other embodiments incorporating its concept may be used. It is believed. therefore, that this inventionshould not be restricted to the disclosed embodiment, but rather should be limited only bythe spirit and scope of the appended claims.

Claims

1. Incombination:

a first strip conductorformed on i first dielectric and spaced from aground plane conductor by the first dielectric, said ground plane being formed on an opposite surface of said dielectric; a second strip conductor formed on cl second dielectric and spaced from the ground plane conductor by the dielectric, said ground plane being dis- posed on an opposite surface of such second dielectric; and coupling means, including a resonant bodydisposed adjacent suchfirst and second strip conductors, for coupling energy between such strip conduc- tors.

2. The combination as recited in claim 1 wherein the first and second strip conductors in combination with the first and second dielectrics and the ground plane provides a corresponding microstriptransmis- sion line.

3. The combination as recited in claim 2 wherein each one of such dielectrically spaced strip conduc tors has portions thereof terminated in an open circuit.

4. Incombination:

a first plurality of spaced conductors; a second plurality of spaced conductors, spaced from such first plurality of spaced conductors; and wherein each plurality of spaced conductors is arranged to distribute signaisfed to such pluralities of spaced conductors through a region adjacentto such first and second plurality of spaced conductors to provide, in responseto such distributed signals, a predetermined magneticfield distribution in such region.

5. The combination as recited in claim 4wherein each one of such plurality of spaced conductors includes a strip conductor disposed on a substrate.

6. The combination as recited in claim 4wherein thefirst plurality of spaced conductors is disposed orthogonal to the second plurality of spaced conductors.

7. The combination as recited in claim 5 wherein such substrates have formed therein an aperture, and wherein such combination further comprises a resonant body disposed within such aperture..

8. The combination as recited in claim 7wherein such resonant body is aferrimagneticmateriaL

9. The combination as recited in claim 8.wherein such ferrimagnetic material is comprised of.yttrium iron garnet.

10. Incombination:

a first pair of spaced conductors, a second pair of spaced conductors spaced from such first pair of spaced conductors; and a resonant body disposed fQr Qoupling energy fed to an input one of such pair of spaced conductors to an output one of such pair of spaced conductors.

11. The combination as recited in claim 10 where- in each one of such pair of spaced conductors includes a strip conductor formed on a substrate.

12. The combination as recited in claim 11 wherein such pairs of spaced strip conductors are orthogonally disposed with respectto each other.

13013. The combination as recited in claim 12 where- 19 in such substrates have formed therein an aperture between such orthogonally spaced pairs of strip conductors and wherein the resonant body is disposed within such aperture.

14. The combination as recited in claim 13 wherein such body is a sphere of a ferrimagnetic material.

15. The combination as recited in claim 14 wherein such ferrimagnetic material is comprised of yttrium iron garnet.

16. Incombination:

a first pair of spaced conductors, a second pair of spaced conductors, spaced from such first pair of spaced conductors; and wherein such pairs of spaced conductors are arrangedto provide a predetermined magneticfield distribution in responseto signalsfed to such pairs of spaced conductors.

17. The combination as recited in claim 16 further comprising:

a resonant body disposed within such predetermined magneticfield distribution to couple resonant frequency energyfrom a signal fed to an input oneof such pair of spaced conductors to an output one of such pairof spaced conductors.

18. Afilter comprising:

an input coupling circuitsuch input coupling circuit including a pair of spaced conductors; an output coupling circuit, said output coupling circuit including a pair of spaced conductors, and said output coupling circuit being spaced from said input coupling circuit; a resonant bodydisposed between such coupling circuits; and wherein such coupling circuits arefurther arranged to provide a uniform magneticfield distribution in a regionwherein the resonant body is disposedto couple resonant frequency energyfed to the input coupling circuit,tothe outputcoupling circuit, through the resonant body.

19. The filter as recited in claim 18 further 105 comprising a pair of sandwiched substrates having a ground plane conductor provided therebetween, and wherein the coupling circuits areformed in mutual alignment on opposite surfaces of the substrates, having an aperture provided through such substrates and ground plane conductors, andwherein the resonant body is disposed within said aperture,

20. The Y1G filter as recited in claim 19 wherein the resonant body is a sphere comprised of yttrium iron garnet.

21. A circuit comprising:

a first radio frequency transmission line having a strip conductor spaced from aground conductor by a substrate, the strip conductor including a first plural- ity of spaced conductors; a second radio frequency transmission line having a strip conductor spaced from aground conductor by a substrate, the strip conductor including a second plurality of spaced conductors; and wherein said first radio frequencytransmission line and said second radio frequency transmission line have the ground plane conductors thereof disposed in a common plane.

22. The circuit as recited in claim 21 wherein the first plurality of spaced strip conductors is disposed GB 2 131 628 A 19 orthogonallyto the second plurality of spaced strip conductors.

23. The circuit as recited in claim 22 wherein each one of the substrates has an aperture thereth rough, such aperture having an end portion disposed between the orthogonally spaced pluralities of spaced strip conductors.

24. The circuit as recited in claim 23 wherein a selected portion of the ground plane conductor of each transmission line has avoid therein and wherein the voids are aligned to provide a common void in the combined ground plane conductor.

25. The magneticallytuned resonant circuit as recited in claim 24further comprising a resonant body disposed through such void.

26. The magnetically tuned resonant circuit as recited in claim 25 wherein the size of such void is selected to provide a predetermined reduction of coupling of resonant frequency energy to such ground plane.

27. A combination comprising:

a first plurality of spaced conductors; a second plurality of spaced conductors spaced from said first plurality of spaced conductors; and wherein each of said pluralities of spaced conduc tors are arrangedto provide a predetermined magne ticfield distribution in a region common to the plurality of spaced conductors in responseto a signal fed to one of such plurality of spaced conductors.

28. The combination as recited in claim 27 where in a first one of such plurality of spaced conductors is orthogonally alignedwith a resonant one of such plurality of spaced conductors.

29. The combination as recited in claim 28 further comprising a resonant body disposed in the region for coupling energy between a first one of such plurality of orthogonally aligned spaced conductors and a second one of said plurality of spaced conductors.

30. The combination as recited in claim 29 wherein such resonant body is a sphere comprising a ferrimagnetic material.

31. The combination as recited in claim 30 wherein said ferrimagnetic material isyttrium iron garnet.

32. A combination comprising:

a first strip conductor having a bifurcated portion disposed on a dielectric; a second strip conductor having a bifurcated portion disposed on a dielectric and spaced from such first strip conductor; and wherein such bifurcated portions are arranged to provide a predetermined magneticfield distribution in a region adjacent the bifurcated portions in response to a signal fed to one of such strip conductors.

33. The combination as recited in claim 32 further comprising a resonant body disposed in such region.

34. The combination as recited in claim 33 wherein such bifurcated portions are coaxially aligned.

35. The combination as recited in claim 34 wherein such coaxially aligned bifurcated portions are orthogonally spaced from each other.

36. The combination as recited in claim 35 further comprising a pair of substrates supporting a corres- ponding one of such strip conductors, said substrates GB 2 131 628 A 20 sharing a common ground plane conductorsandwiched between such substrates; and wherein an aperture is provided in such substrate and ground plane conductor providedwithin the periphery of such bifurcated portions of such strip conductors.

37. The combination as recited in claim 36 further comprising a resonant body disposed in such aperture.

38. In combination:

a pair of microstrip transmission lines, having a common ground plane conductorand having strip conductor portions formed on upperand lower portions of each microstrip transmission line and having a void formed in such common ground plane and having an aperture through such microstrip transmission line aligned with thevoids; a resonant body disposed in such aperture; and wherein the size of such void is selected to provide a predetermined electrical relationship between such resonant body and such ground plane conductor.

39. The combination as recited in claim 38 wherein the size of such void is selected to provide a predetermined reduction in resonant frequency ener- gy induced into said ground plane conductor.

40. A method of reducing spurious energytransfer in a magnetically tuned resonant circuit corn prising the steps of:

providing a coupling circuit having a plurality of selectively spaced conductors; providing a signal to each of such spaced conductors; distributing a magneticfield generated in response to such signal in thevicinityof such conductors in accordance with the number of and arrangement of such conductors.

Printed for Her Majesty's Stationery Office by TheTweeddale Press Ltd., Berwick-upon-Tweed, 1984. Published atthe PatentOffice, 25 Southampton Buildings, London WC2A lAYfrom which copies may be obtained.

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